As requested by TRC and others, here come the Full Combat Loads for all the Tau units, from the original 3e codex, the 4e codex, and Imperial Armor 3.  The entirety of this may take some time, since I also need to study for my college classes, but I figured I'd get the ball rolling.

I'm going to ignore the HQ units (Ethereal and Shas'o/'el Crisis team), unless there's a specific request for them.

Also, I'm going to include the Apocalypse formations for the Tau, with a general view of what their special rules are.  This is mostly for formation names, but sometimes the composition is good as well.

To keep this simple, I'm going to just put one unit per post, so if you have questions, please at least quote the unit name.

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"For the Lion and the Emperor!"

Let's start with the PBI, the humble Fire Warrior.

The basics haven't changed between 3e and 4e; you have to take at least one unit of Fire warriors, which must be between 6 and 12 strong.  They are all armed with a Pulse Rifle, and can also carry photon grenades and/or EMP grenades.  Photon Grenades negate the +1 attack for charging, and I always pay the points for them.  A unit of FW in cover and equipped with photon grenades can actually deal with Genestealers, tying them up for some time.  I don't take EMP grenades all the time, unless I'm tooling squads for extremely aggressive use close to enemy vehicles.  EMP grenades are so good they should really give the FW a macro-weapon attack against vehicles in Epic terms, but they do nothing against infantry or Monstrous Creatures like Carnifexes.

In 3e, up to half your FW squad could replace their Pulse Rifles with Pulse Carbines, which have an integral photon grenade launcher.  Carbines cause Pinning in 40k, but only have an 18" range and are Assault 1 weapons.  Assault 1 means that no matter how far you move, you always get one shot up to 18".  Pulse Rifles are 30" range Rapid Fire weapons, which means that if the unit stands still, they can shoot once at 30", or they can shoot twice at 12" if moving.  In 4e, any number of models could be equipped with Carbines.  I still prefer to only use rifles, since the extra shot per Tau really makes everyone wince when the dice start flying.

Character:
The Shas'ui in charge of the team can be given a Markerlight, and can also take items from the armory.  In 3e, there wasn't anything worth taking after the Majority Armor save ruling (Gun drones aren't really worth fielding in my book, since I bring mechanized FW).  In 4e, with the changes to Markerlights, there is something I'd be willing to trade 2 Pulse rifle shots at range for:  A pair of Marker Drones, which have Networked Markerlights.  Networked Markerlights can benefit the unit they're in, which is something that Markerlights cannot.  This is NOT necessarily a given, however, as when I'm on the move with "Fish of Fury" I lose the Markerlights (they're Heavy Weapons, which cannot move and shoot, even when on a drone).  I would bring the Marker Drones if the FW were walking or being Orca-dropped into position, but writing that into Epic would require a unit special rule.

Transport:
Fire Warriors can be given a Devilfish Transport.  Before 5th edition's nerf to vehicles, I used what is often called the 'Warfish' loadout as my basic transport:  Devilfish (which comes stock with a burst cannon), Smart Missile System (and a vehicle Multi-Tracker), 2 Seeker Missiles, and Decoy Launchers.  Now that the Smart Missiles are no longer considered Defensive Weapons, I'd use Gun Drones and add Sensor Spines and a Disruption Pod.  This raises the survivability of a basic Devilfish dramatically, since it will be hiding IN terrain, counts as an Obscured Target at range if it isn't in terrain, and you have to re-roll immobilized results on the damage table (which would be fatal to a moving skimmer).  Interestingly enough, this is much more heavily equipped than the example Devilfish in Imperial Armour 3's historical scenarios.

Troops:
Fire Warriors are a Troop choice in the Tau army, competing against Kroot.

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"For the Lion and the Emperor!"

Next up is the Fire Warrior's friend, the Pathfinder.

Pathfinders come in units of 4-8, and are armed with Pulse Carbines and Markerlights.  They can be given the same grenades as Fire Warriors.  They also come with a Devilfish.  After the Fire Warrior game for the PS2 came out, GW added an option for a Rail Rifle in a White Dwarf article.  The full railrifle wasn't very useful, as it had a bad habit of killing users who were using the "shoot someone other than who your unit is" option.  In 4e, up to 3 Pathfinders can have railrifles (in place of their Carbine and Markerlight), and don't suffer from the 'Gets Hot' rule anymore.

Pathfinders have the Scout Universal Special Rule, which allows them to move after deployment but before the game actually starts.

Character:
Like the Fire Warriors, the Team Leader can be upgraded to a Shas'ui, who can then take items from the armory.  I would take Marker Drones with a 'Sniper squad' of the Team Leader and 3 Rail Rifles.  The Team Leader can use his non-Networked Markerlight to call Seeker Missiles, while the Marker Drones help the Rail Rifle-armed Snipers.

With the new Markerlight rules, Pathfinders are very popular, and are often used to camp on an objective in 5e, relying on their long range to keep enemies away.

Transport:
As I've already mentioned, PF must take a Devilfish in 40k.  I usually didn't take as many upgrades, as the "P-fish" was not supposed to be in combat.  The P-Fish usually just had a couple Seeker Missiles and the Decoy Launchers.  In 5e, I'd take a Disruption pod instead of the Decoys.

Fast Attack:
Pathfinders are a Fast Attack choice in 40k, which means that they are competing against Gun Drone Squadrons, Piranha squadrons, Vespids, and Tetra squadrons.

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"For the Lion and the Emperor!"

Now, we have Crisis suits.

A team of Crisis Suits numbers between 1 and 3.  Each suit can take up to 3 weapon and support options, with twinlinked weapons taking two "slots".  Crisis can be armed with Burst Cannon, Flamer, Fusion Blaster, Missile Pod, or Plasma Rifle, and can also have supporting systems like Shield Generators or Drone controllers.  There are other systems like Thermal Imaging and targeting equipment, but those don't really matter at the Epic level (sure do matter at the 40k level, though).  There are a LOT of possibilities for armament, and a scan of a 40k Tau forum will net pages of topics talking about the optimum loadout for suits.

There was an article in White Dwarf shortly after the Tau came out, talking about different suit loadouts.  I can't find my copy (should be WD266 or 267, US version), but the general idea was that there are two schools of thought for arming Crisis suits.  Either you have a team where one suit has the perfect weapon for one task, and that suit's weaknesses are covered by his teammates, or the entire team specializes in one role.  Way back when, JimmyGrill decided that the Crisis suit loadout we would use was one where each member of the team specialized, instead of having specialized teams.  I prefer the Jack of All Trades decision for Epic, as it saves a lot of arguments.

Our assumed Crisis team is 3 members, one armed with a twinlinked Fusion Blaster (equivalent to a meltagun), another armed with a twinlinked Plasma Rifle, and a third armed with a twinlinked Missile Pod.  This particular assumed loadout does not include support systems like gun or shield drones or shield generators.  As it is, there are already 6 wounds (Crisis suits are 2 wounds each) on each base.  Putting Shields on each Crisis suit would make them almost impossible to kill with antitank weapons (the preferred way to kill suits).

Elites:
Crisis Suits are an Elites choice, competing against Stealth Suits.

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"For the Lion and the Emperor!"

Stealth Suits.

Stealth teams number between 3 and 6 members.  Each one wears either an XV15 (metal models) or XV25 (plastic) Stealth Suit, which is similar protection to a Marine's power armor.  On top of that, they have a Jet Pack, which increases their speed, and they have a Stealth Field, which means that average detection range is 21", and Max detection range is 36".  The suits are each armed with a Burst Cannon, and up to 1 in 3 can take a Fusion Blaster for tankhunting.  They can also take battlesuit support options, but that makes the unit very pricy very quickly, without really increasing their killing power.  

Stealth Teams Infiltrate, allowing them to start closer to the opponent.

Stealth Teams have 2 attacks on their profile and are Strength 4.  A full Team is roughly on par with a 5-man Space Marine Assault Squad in close combat, except for the low initiative and lack of frag grenades to force the opponent to strike simultaneously.  I have won combat when I charged an assault squad with a 6-man Stealth team after shooting them up first (roughly 8 on 6 odds when I went in).

Character:
The Team Leader can also take a Markerlight, and has access to the armory for additional gear.  I would not take any Markerlight-equipped units, as Stealth Teams are best when used very aggressively and on the move.

Elites:
Stealth Teams are Elites, competing with Crisis Teams.

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"For the Lion and the Emperor!"

Tanks!

The Hammerhead is one of the most dangerous tanks in the 40k game, although it's less dangerous now with the 5e defensive weapons nerf.

As a baseline, it has similar armor to a Predator (13-12-10, compared to the Pred's 13-11-10).  Then you start adding things to keep the HHead alive and killing things, and it very rapidly becomes one of the most survivable tanks in the game.  Always under a 4+ cover save, able to hide in terrain without having to make Dangerous Terrain tests, and forcing any engine damage to be re-rolled (making the tank nearly unkillable on a glancing hit (1/36 chance of engine damage killing the HHead, as opposed to any other skimmer's 1/6).

Now, let's talk about weapons:  
The Ion Cannon is 60" range, Strength 7, AP3 (punches power armor like that's it's job), 3 shots.  That's 25% more range, same strength, better AP value, and 50% more shots than an Autocannon.  All of this is really impressive, until you look at the Railgun.

The Railgun (on a Hammerhead) has 2 fire modes:  Solid Shot, and Submunition.  Both have the same range, 72".
The submunition is a Strength 6 AP4 large blast.  This is comparable to a Whirlwind or a Griffon in 40k.  This mode is ideal for removing hordes of infantry, especially with the 5e blast weapon rules (always scatters somewhere).

The Solid Shot is a dedicated vehicle killer.  It's a Strength 10 AP1 single shot.  It reliably punches Land Raiders and Monoliths 1/3 of the time (AP1 weapons no longer auto-penetrate, but are instead more likely to kill the vehicle.)  A Rhino can't even stop the shot under 3e/4e vehicle rules.  Sadly, the Cheddar Eldar have equipment that can largely ignore this powerful weapon.  Against any other race, the Railgun is the king of the vehicle-mounted weapons for the purpose of killing other vehicles.

and the IA3/Forgeworld weapons:
twinlinked longbarrelled burst cannon:  36" range, S6 AP4, Assault 3. (why?  Ion Cannon is better.)
Missile Pods:  36" range, S7 AP4, Assault 4. (half the range of an Ion cannon, worse AP, more shots)
Twinlinked Fusion Cannon:  24" range, S8 AP1, Heavy 1 Blast Melta. (painfully short ranged, but might be useful for vehicle killing)
Twinlinked Plasma Cannon: 48" range, S7 AP2, Heavy 2. (Ion cannon is better range and has one more shot, but this kills Termies)

I'm also going to talk about the Skyray here, since the base chassis is the same.

The Skyray originally appeared in Imperial Armour 3 as a Seeker Missile platform with some capability against aircraft.  It carries 2 networked markerlights, and 6 missiles.  Additionally, it cannot carry more seeker missiles, while almost every other vehicle in the Tau force can.

It's worth mentioning that under the 40k Seeker rules, you need to first hit the aircraft with a Markerlight (on 6s, unless it's the Skyray's OWN markers, then 3+), then you need to hit with the Seekers (IA3: 4+ vs aircraft).  The effective AA markerlight bubble around a Skyray in 40k is only 24" (usually translated to 30cm for special weapons), and significantly reduced effectiveness within 24" around any other unit.

Then there's the secondary weapons systems, which applies to both the Hammerhead and Skyray:
In 4e, you have 3 choices:  2 Burst Cannon, a Smart Missile System, or Gun Drones.  Please note that there are 2 burst cannon, not one twinlinked.  They're all pretty much the same, except that the Gun Drones are considered passengers that can fire out using their own ballistic skill, not vehicle-mounted weapons.  My preference has always been the Smart Missiles, but any attempt to have mobile armor in 5e requires you to use Gun Drones if you want to fire everything on the move.

Heavy Support:
The Hammerhead and Skyray are Heavy Support choices, competing with each other, Broadsides, and Sniper Drone teams.

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"For the Lion and the Emperor!"

Broadsides are the heaviest battlesuit version available.

It is worth pointing out that a broadside has an infantry statline in 40k, although CS seems set on counting them as LV (weapons assume one per base).  This is most interesting because Broadsides are more likely than Crisis suits to hole up in buildings in 40k, but are not allowed to enter buildings in Epic.

Broadsides are Crisis suits that have traded their mobility for better armor and bigger weapons.  They are the true tank-killers in the army.  All the comments about the railgun Solid Shot apply to the Broadside suit.  Broadside suits carry a twinlinked railgun (that cannot fire a Submunition) and either a Smart Missile system or twinlinked plasma rifles.

The SMS or TLPR exist to keep infantry away from the Broadside so it can continue killing tanks.

Broadside suits also have space for one support system, and I often use the Advanced Stabilization System on broadsides armed with SMS.  The StabSys (sorry, not abbreviating that system normally, I don't think the swearfilter will like me!) allows the Broadside to move and fire heavy weapons, although you then suffer from the Slow and Purposeful rule (always move as if in difficult terrain).  I do not use that system on broadsides with a plasma rifle, since the broadside can move and fire the plasma normally.

Heavy Support:
Broadside battlesuits are Heavy Support choices, competing with Hammerhead, Skyray, and Sniper Drone teams.

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"For the Lion and the Emperor!"

As are Space Marine Attack Bikes. Essentially they are Infantry with special move and shooting rules.

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We are returned!
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Sniper Drones are an addition in the 4e Tau Empire codex.

They consist of one controller and 3 sniper drones.  The controller has a networked markerlight, and the sniper drones each have a Rail Rifle.  Additionally, the entire unit has the same Stealth Field that Stealth suits have.  The Sniper team has a huge advantage over the Stealth Suits, however.  The Sniper Team's weapons are all 36" range, so they can stay away from the enemy and plink away, when the enemy is unlikely to be able to fire back at all, while the Stealth Team must close to within 18" to engage the enemy.

Sniper Drones are limited in deployment, up to 3 teams can be taken as one heavy support choice, but no more than one choice can be Sniper Drones.

Heavy Support:
Sniper Drones are Heavy Support choices, competing with Hammerhead, Skyray, and Broadsides.

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"For the Lion and the Emperor!"

Carnifexes, Hive Tyrants,...

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We are returned!
http://www.epic-wargaming.de/

Point taken, although Monstrous Creatures could be multi-DC war engines. (Can't hit them with any one weapon and get rid of them, after all)

Since my biggest issue with Broadsides as LV is the fact that broadsides can't hide in Epic like they can in 40k, it's really a minor non-issue at this point.

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"For the Lion and the Emperor!"