I have an ATi Mobility 200M, and I can play Diablo II on it with no lag.
Seriously, though, it can play Unreal Tournament 2004, and that pushes it some. It can play GTA: Vice City, though, Sacred, Aliens Vs. Predator II, and some other older games like that. I tried putting Quake 4 on it... It worked, but the screen wouldn't load completely. I mean the game screen... Half of it was loaded and half of it wasn't. I had about an average of one frame per twenty seconds.