i was talking with some people in the [NO] server and they started rambling about how macs had no games and how they sucked... so i decided to do a search on a mac port of Gmod (garrys mod) and i found this:
http://www.codeweavers.com/products/cxgames/
you can run steam and other windows games on a mac
take that!

Plenty of stuff even without crossover, although it appears that there is a huge decline in stuff being released recently

hmm... it doesn't work if your mac is powerpc based :/

Damn =\