The old version of the Epic Proxy List was about four years out of date, so here is a new one, separated by manufacturer and faction. I'll try to add links where I can, but no promises. If you have your own list of proxies, please feel free to post it. However, this is a thread for proxies from non-GW manufacturers of 6mm products; it is not for forumware.
Exodus Wars Khazari - Most Useful for Squats and Imperial Guard
Khazari - Squats
Kamikaze Droid Swarm - Necron Scarabs, Tau Drones
War Droid Swarm - Squat Robots, Ork Killa Kans
Road Warrior Patrol - Squat Bikes
Raider Patrol - Ork Buggies, IG Sentinel, Squat Buggy, IG Tauros, IG Tauros Venator
Trike Patrol - Squat Trikes
Valkyrie Patrol - IG Vulture, IG Valkyrie Sky Talon, Squat Gyrocopter
Valkyrie MkII Patrol - IG Vulture, IG Vulture Punisher, IG Valkyrie Sky Talon, Squat Gyrocopter
Valkyrie Transport Squadron - IG Vulture, IG Vendetta (with Valkyrie MkII cannon)
Exodus Wars Guild - Most useful for Imperial Guard and Space Marines
Achilles MBT Troop and
Achilles MBT Squadron - IG Leman Russ, SM Predator
Agamemnon Command/FAO Detachment - IG Salamander (Scout or Command)
Apollo SPA Battery - IG Basilisk
Assault Centuria - IG Elysians, SM Assault Marines
Bounty Hunter Snipers - IG Snipers
Bounty Hunters - Eldar Rangers, Eldar Exodites
Cerberus MRL Battery - IG Manticore, SM Whirlwind
Cyclops Heavy Mortar Battery - IG Griffon, IG Bombard
Elektra Heavy Tank Squadron - IG Shadowsword
Enforcer UPC Squadron MkI and
Enforcer UPC Squadron MkII - IG Baneblade
Exterminator Heavy Tank Squadron - IG Stormhammer, IG Stormlord
Hector AT IFV Detachment - IG Chimaera, SM Lascannon Razorback
Hoplon Transport Squadron - Ork Battlewagon
Icharus SPAAG Battery - IG Hydra, SM Hunter
Legionnaire Centuria and
Legionaire Combat Squad - IG Guardsmen/Fire Support, Tau Human Auxiliary, IG Storm Troopers, SM Space Marines/Devestators
Legionnaire Support Squad - IG Fire Support, SM Devestators
Mounted Bounty Hunter Patrol - IG Rough Riders, IG Tallarn mukaali rough riders,
Eldar Exodite Jetbikes, Eldar Exodite Shining Spears
Myrmidon Centuria and
Myrmidon Squad - SM Terminators, SM Space Marines
Orbital Deployment Pods - SM Drop Pods
Paris AP IFV Detachment - IG Chimaera, SM Heavy Bolter Razorback
Phalanx APC Squadron - SM Rhinos
Prefect Precinct and
Prefect Patrol - Adeptus Arbites, IG Guardsmen, Chaos Marauders(Cultists)
Prefect Rapid Response Patrol - IG Rough Riders, SM Scout Bikers
Prefect Sniper Teams - IG Snipers, SM Scouts
Prometheus Flame Tank Troop - IG Hellhound
Shadow Knight Cell - Chaos Cultists, Chaos "Forlorn Hope", Space Marine Scouts
Support Centuria - Ork Big Gunz, IG Weapons Platforms
Trident Tank Hunter Squadron - IG Leman Russ Tank Destroyer, SM Sabre Tank Hunter
Exodus Wars Edenites - Most useful for Necrons and Chaos
Assault Infantry - Necron Pariahs
Assault Sergeant - Necron Lord
Assault Squad - Necron Lords and Pariahs
Carrion Swarm – DE Razorwing Flock
Heavy Infantry and
Heavy Support Squad - Necron Immortals
Infantry Squad - Necron Warriors and Immortals
Infiltration Infantry - Necron Flayed Ones
Jump Infantry Squad - Chaos Raptors
Rifleman - Necron Warriors
Walker Squad - Chaos Dreadnoughts
Zombie Horde - Chaos Zombies
Exodus Wars Royal Empire - Most useful for Imperial Guard
Assault Platoon - IG Storm Troopers, Chaos Berserkers
Heavy Weapons Platoon - IG Fire Support, Heavy Weapons for IG Infantry
Infantry Company - IG Infantry, IG Siege Infantry IG Krieg Infantry, etc.
DRM Pax Arcadia - Most useful for Imperial Guard
Light Infantry - IG Infantry
AT Infantry - IG Fire Support Platoon
Special Forces - IG Storm Troopers
Standard Infantry - IG Tallarn Infantry
Industrial Infantry - AdMech Tech Priests, AdMech Skitarii
Scout Infantry - IG Snipers, Marine Scouts w/ Sniper
Jungle Troops - IG Catachan Infantry, IG Hive Ganger Infantry
Sniper - IG Snipers
Reg HQ - IG Commanders, IG Supreme Commanders
Valiant - SM Rhino
Hammerjack - IG Griffon
Chasseur - IG Leman Russ, SM Predator
Buggy 1 and
Buggy 2 - Ork Buggies, IG Sentinel, IG Tauros
Firewall - IG Hydra
Cruiser - IG Chimaera, IG Seigfried
Mammoth - IG Ragnarok
Petard - IG Manticore, SM Whirlwind
Bastion - IG Baneblade
Thunderstrike - IG Minotaur
Human Light Vehicles - alternate Sentinel
DRM Andrayada - Most useful for Necrons, Chaos
Andrayada Commander - Necron Lord, torso of Destroyer Lord
Body Guard - Necron Pariahs
Infantry Phalanx - Necron Warrior, torso part of Necron Destroyer, Chaos Marine, Chaos Chosen
Heavy Phalanx - Necron Immortals, torso part of Necron Heavy Destroyer
Scouts - Tau Firewarriors, Eldar Warp Spiders
Vanguard - Tau Pathfinders
Vultures - Chaos Raptors
Hubries Variant 1 and
Hubries Variant 2 - Necron Destroyer Bodies?
Vorace - ATML Knight Lancer
Velite - SM Dreadnaught, Chaos Dreadnaught, Tau Battlesuit
Verger - SM Dreadnaught, Chaos Dreadnaught
Majestic - ATML Warlord Titan (with added carapace weapons)
Majestic Weapons - ATML Optional Titan Weapons
Malignant - ATML Warhound
Mordent - ATML Reaver
Valkalon - Eldar Nightspinner, Eldar Falcon Hull
Vertex - DE Barge of Pain
DRM KraytonianKamalei - Kroot
Kraytonian Light Infantry - Slann, Chaos Mutants
Kraytonian Medium Infantry - Slann, Chaos Mutants
Kraytonian Heavy Infantry - Slann, Chaos Mutants
Ketzali - Slann Priest, Chaos Cultists, Skaven
Ketzali Command - Tau Firewarriors, Tau Ethereals
Karrok II - Tau Firewarriors, Tau Ethereals
Rakkat Rider 1 and
Rakkat Rider 2 - Eldar Exodite Dino Rider
Torakk Riders Variant 1 and
Torakk Riders Variant 2 - Eldar Exodite Cavalry, Eldar Shining Spears, Dark Eldar Reaver Jetbikes
Kijakk - Eldar Vyper Jetbike, Tau Tetra
Kurall - Eldar Hornet, Tau Pirahna
Arkator Bomber - Chaos Helltalon
Arkiten Fighter - Chaos Swiftdeath, Chaos Hellblade
Araspan - Chaos Harbinger Bomber
Elohe Raiders Variant 1 and
Elohe Raiders Variant 2 - Eldar Exodite Flyers, Eldar Exodite Scouts
A couple notes about Kraytonian Infantry. The Light, Medium, and Heavy Infantry all have the same two basic sculpts, and are defined by their heavy weapons. The Karrok II package comes with 39 Personal Guard in two sculpts (useful as Firewarriors) and one "Karrok II" commander (a good Ethereal), and the Ketzali Command has 32 Personal Guard of the same sculpts as the Karrok II package, and 8 Commanders (also good Ethereals).
DRM Skyth - Most useful as Tyranids
Critters/Defenders - Tyranid Termagants, Chaos Daemonic Beasts
Leapers - Tyranid Gargoyles, Chaos Harpies
Claw Beasts - Tyranid Lictors
Worker Beasts - Tyranid Termagants
Vampire Beasts - Tyranid Genestealers
Skyth Beasts 1,
Skyth Beasts 2,
Skyth Beasts 3 - Tyranid Carnifexi