True20 has the Lux Aeternum setting. Its a swashbuckling space opera type deal - think the three muskateers in space. Not bad.
There is the Serenity game, built around Firefly. I've heard bad things about the ruleset though (but anything firefly can't be all bad).
D20 traveller is something I'm going to have to purchase.
If you want really light, you could take a look at the PDQ rules (ruleset from Atomic Sock Monkey). I'm looking at Zorcerer of Zo, and Truth & Justice, and this ruleset looks really intriquing for a GM who hates prep. They don't have a science fiction setting though - but if you look at Zorcerer, and see how little prep he did for that, and how well it worked... well, you could wing it pretty easy, I think.
There is the Serenity game, built around Firefly. I've heard bad things about the ruleset though (but anything firefly can't be all bad).
D20 traveller is something I'm going to have to purchase.
If you want really light, you could take a look at the PDQ rules (ruleset from Atomic Sock Monkey). I'm looking at Zorcerer of Zo, and Truth & Justice, and this ruleset looks really intriquing for a GM who hates prep. They don't have a science fiction setting though - but if you look at Zorcerer, and see how little prep he did for that, and how well it worked... well, you could wing it pretty easy, I think.