I was wondering what cool games there are that run on Mac. I was thinking of major games, like Warcraft III and Unreal Tournament '04 (both I have), not simple internet download games. Thanks!

It depends on what you like, how old you're willing to go, and whether you count emulation and virtualisation strategies.

Relatively recent games that run natively include Civilization IV, Age of Empires III, Bioshock, The Sims 3, Lego Batman, Aquaria (indie title but certainly not simple), Quake IV, and Call of Duty 4. There are lots more I could list if you really want.

Wikipedia has a good - albeit incomplete - list of Mac OS X games that may be of some use
http://en.wikipedia.org/wiki/Category:Mac_OS_X_games