While this list is part of the MacRumors.com web site, it is undoubtedly more factual based than some of their other postings. The site lists over 60 games that can be run in Mac OS X.
The listing has are in alphabetical order and include a link to a download as well as notification as to if it is Universal and a brief description of the game.
Some Examples: (Yes means Universal)
Alex the Allegator 4 No A 2D side-scrolling platform game that imitates the look and feel of the green screen Gameboy.
AsteroidsQC No A Quartz Composer asteroid game as a developer example, requires the Mac OS X developer tools to be installed.
Yes An RPG, inspired partly by the Phantasy Star series of games and partly by Legend of the Green Dragon, a web-based free RPG.
Freeciv Yes A highly customisable civilization game based on Civilization 2
Glider Pro No An arcade paper aeroplane simulator.
Marathon Trilogy No The Original FPS Trilogy from Bungie Studios. Runs on Mac OS X via Aleph One project.
Pac the Man X Yes A Pacman game for Mac OS X.
Wolfenstein: Enemy Territory Yes Enemy Territory is a first person class-based shooter set in World War II and based on the Return To Castle Wolfenstein Engine (Quake 3)
For a complete list and the links to the games click here.