There's also:
Oni (first OS X commercial game, don't know how well it runs on later OSes)
Giants: Citizen Kabuto (I've run it under Leopard, YMMV)
Knights of the Old Republic (has speed issues on Dantooine, poor port)
Jedi Knight (Dark Forces III)
Jedi Knight II: Jedi Academy
Max Payne
Halo
Aquaria (new game, runs perfectly fine on my 1.5 GHz PBG4)
There's also console emulation for NES, Genesis, SNES, etc (N64 and up is too much for a computer of your speed in my experience) if you already own the games. If you have some old DOS games, you can play most of them in DOSBox.