Where can I find Free Games for my iMac?

I have noticed there are not many games out there for Macs. Maybe I haven't researched enough, but I have noticed there are a lot of Games you can buy for PCs, but not that many for Macs. There are also a few websites that offer free gaming online, like Yahoo!, but some of the games that you can Download for Free are only good for PCs not Macs. Where can I find cool games, downloadable, for Macs.