yeah the only ones can think of are World of Warcraft and Everquest Mac. Runescape of course can play on Mac. Not many others than that, so if you own a mac and want to game World of Warcraft is your best bet.
Planeshift works on macs :S (its REALLY BUGGY but the community is good and its gonna be good someday .... and will be free :P ) (and i like the mining, melting, stocking, heating, forging system :P )
dude ur nuts i'm working on an imac 5,1 u know the mac where everything is in ur screen. Well i use it to make architectural drawings and it runs reaaaaalll smooth. If i do the same on a pc with same hardware it would just lagg and the company i work for all use mac. The diff between PC and Mac is PC is for home usage mainly and mac is for business purposes. And Mac pwns cause they have less viruses then pc. The software is much more developed.
Ow Yeah and Windows sucks. WINDOWS VISTA IS RIPP OFF FROM MAC.
on topic: One of the best free mmorpg's available for mac is shadowbane, there is also world of warcraft and second life, ...
But i suggest using an windows emulator if u really wonna play diff games