Two great games are coming to Apple Macintosh and will run on OSX natively. The games are Gears of War and UT3.
In an interview with Spike TV's Game Head, Mark Rein revealed that both games are in development for OSX. As a reason for both 'Windows Games' also coming to the Macintosh platform the vice president of Epic Games said: "We're an independent company and we make engine technology. Don't forget, we're also doing Macintosh." and a little later "Yes, Gears is coming to the Mac and so is UT".

Now this must be music to Mac-shooter-fans!

The Unreal Engine is being developed as a universal binary (stated in this article) so that means that the game will also be available for PPC based machines.

Source: Inside Mac Games