Heya!
As a Mac user myself, I feel that there should be more poker rooms out there supporting our beautiful OS X. So far there aren't that many, but here are the ones that work on a a Mac and have a
rakeback deal.
Full Tilt offers the option to download their software. I personaly use it and it works pretty well.
Absolute Poker has a no-download java version. I have never tried it, but it looks as though it's good.
There are some other poker rooms that have java versions of their software, but they currently do not offer any
rakeback deals.
Another option is to use a software like Parallels for Mac, that allows you to run Win XP (if you have a license) on your Mac. I use it on my powerbook to run Windows Vista (slow) and Ubuntu (quite good)