Team Fortress 2.
I might try Lost Horizon. But I hear it's a bitch on your computer, even with high-ish specs. Shattered Horizons. It actually runs very well on my system, and it's okay, but I don't think I'll buy it. Maybe if it drops to $5 some time, but the game itself just falls rather flat once you get past the initial gravity situation. The zero gravity is cool and all, but the weapons are unimaginative and boring, and the Cthulhu damn recoil or whatever the fuck it is is awful on every weapon but the pistol. It is pretty beyond all reasonable hate, however.