It seems like linux gaming is finally becoming a reality. So far most games seem to be simple ones (not that that makes them bad – the linux card games are far superior than any windows ones I have seen) or multiplayer based (few have good AI’s).
Linux Gamers have a review of Open Source 3D Shoot-em-ups
While Linux Journal has a more general review of Free Games for Linux
I really need to get my 3d card running properly again, as some of those mutliplayer shoot-em-ups look rather good, and I definitely need to try out that racing game!