I will always be up for a game of RTCW:ET (probably my favorite LAN party game). Lately I have been playing some Doom 3 and some UT2004, but I have fallen back to my old favorite; Warcraft 2 (using the Stratagus engine).
I'm a hardcore Starcraft Brood Wars fan, even though its windows only, it works good enough with cedega. I also like Warcraft III which works perfectly in cedega I haven't found a boat load of good linux native games, but I certainly do enjoy quake 3, quake 4, and unreal tournament 2004. Hopefully Quake Wars will be as enjoyable as the others