Our two Macintoshes (Mac mini and MacBook)have the same integrated graphics solution (GMA 950), so here are some games I play:
Playable, but fun (settings had to be reduced, and don't look very pretty):
Unreal 2004
Halo
Myst IV (Myst IV runs in Rosetta and is thus slow)
Myst III (Myst III also runs in Rosetta, and cinematics are a bit choppy)
Deimos Rising (music can get choppy)
Great (at full settings):
American McGee's Alice (with Universal Binary)
Elite Force Multiplayer Universal Binary
Quake 3
OpenArena
Wolfenstein Enemy Territory
OttoMatic
Unreal Tournament X