I am seeing a lot of discussion about factions but it seems the ideas or more valid as expansions.
I think the main factions could be (should be):
A) Empire: Storm Troopers and support led by various generals and/or, notably Vader.
B) Rebel Alliance: Combination of various species from rebel systems with the core being the troopers currently being released
C) Trade Federation: Droids of all Clone Wars flavors led by the likes of Dooku, Grievous, "Tarantula Guy", or robot. Genoshans?
D) Republic: Clone Troopers and support led by Jedi Knights.
The way I see it, generally, Droids would be the worst and cheapest primary choice, then Storm Troopers, then Clone Troopers. Rebels would be an interesting mix. Their stats across the races need to be quite good to usher the "small rag-tag band of freedom fighters" feel. Of course, Ewoks should be chaff.
Expansions of bounty hunters, assassins, Grey Jedi, Sith Assassins, Mandalorians (Death Watch / different houses etc.), double agents, & general Scum, would be a great way to get more iconic SW characters into a variety of faction lists.