I'm gonna start spriting a new faction, dunno though. It seems to me like all the fan-made factions have basically the same feel, unlike most RTSes, where each race makes you play differently. Help me brainstorm some original faction.
1: Zombies. You can't buy zombies. Only zombie spawners. They are really tough but only have melee weapons. Game start is really weak, but later, you have massive hordes.
1.5: Zombies 2: Spawn a lot always. Endless horde of weak units.
2: Invincibles. Similar to zombies. But lots of turrets and base defense. Has 1 main spawner. Can buy priests or whatever to augment spawner. Move vvveeerrrryyy slowly. Very slow, wide area diggers. When these units die, they drop a corpse which spawns into a new invincible in a matter of minutes. Rebirth drop thingy is indestructible. Maybe unit limit?
3: Totally not dutch from AoEIII. Instead of diggers has money spawners.
4: Resistance. Like what someone was thinking for ronin. You call for "an expedition ship" costing a certain amount of money, maybe different varieties. It'll give you random stuff. Maybe lots of actors, maybe lots of weapons, maybe some diggers, maybe not.
5: Bugs. Mother ant deep underground. Digger ants evolve by eating ground. Mother spawns new units.

But these are all lame, what can you guys think of?

Angels and demons.

Super-scientists

Superheros/villians

Space monkeys (not literally a monkey....)

i dunno.

Um, those are just different skins of the same idea, of thinking of stuff that changes gameplay.

Tee hee orignal is moose in French. I'm afraid to say, this is just not as cool as a moose faction.

It's funny that you mention that, my friend released a mod called Moosecorp.
Also: I'm dumb.

MOOSE FACTION: make them out of ACrabs, and give them antler weapons.

It could be a whole new game mode! Make it so you aim a gun with the mouse (first person shooter style) to try and blow up these moose. So it's like Big Buck Hunter with cortex command's engine!

you could make them ram people!

Allright, how about making a list of already-done factions? Here is my compiled list...

-Futuristic laserific army with mechs (AAL)
-Robotic corporation (DSTech, Crobos, Tek?)
-Zombie (Undead Apoc)
-Futuristic Japanese corporation (DarkStorm/Tengu)
-Russian Army (Bear Fed)
-Not-so futuristic army, but still with mechs (Pelian, Kloveskan)
-Medieval (Melee Master Arms, WizCorp)
-Coalition-style foot soldiering army (Coalition, Diemos, Red Gear Army, NVC, UniTec?)
-NASAstronauts (Emporeans)
-Roman Legion (Legio Machina)
-Game-ported (Space Marines, Ork Boyz, Helghast, upcoming Necrons, Enclave)
-Tribal (Allen's unfinished Raven Bear Snake)

Let me have what you think of this categorization.

how about a faction that doesn't use weapons, but instead has laser eyes.

nobody's made a Voodoo faction yet...

there's a reason. to much lua. Lua voodoo. and besides, if someone would say something tacky like 'do that voodoo that you do so well' and then the forums will implode. the closest we could really do without massive lua work, is the fetishes/little voodoo guys from Diablo 2. and there just annoying. annoying with firebreath.

Laser eyes is perfectly possible with lua, you could bind different keys to it and the actor sends out a beam from their head when you push a button, maybe laser eyed crabs?

How about a faction that only uses melee - they will have enhanced speed and flight to make up for no guns. Or a faction that only uses thrown weapons/grenades. Or plants vegetables.

Or how about a wolf faction - ACrabs with Lua so that jumping raises them up slightly and makes them lunge towards the aim angle, whilst firing damaging particles. Heavies consist of more armour and Elites have turrets mounted on them.

How about a vegetable faction?
Killer tomatoes, chainsaw-wielding carrots, that kind of stuff.