The currently sold rulebook is the latest, v1.5. This can also be downloaded from the website.
Armada is still the same and can also be downloaded or bought.
On the SG site you can download the following official rules as well:
The following has all Official PDF's, every other pdf not in this list is not official:
http://www.specialist-games.com/battlef ... lebook.aspThese pdf's are thus official but not sold:
Yriels Raider (Flame of Asuryan)
Doom of the Eldar (Craftworld Eldar)
Ships of Mars (Adeptus Mechanicus)
Powers of Chaos (Terminus Est - Nurgle Chaos fleet)
Fabric of the Imperium (Rogue Traders)
There is also the latest FAQ (1.5).
Special note, on mentioned website you can download the Forgeworld Tau rules (also on FW site). These are the rules from IA3:Taros Campaign + fleet list. They are under experimental rules but wide accepted as the official ones.