Anyone know of any good ones?

WoW is free up to level 20 and I could run it on my Macbook fairly smooth.

City of Heroes isn't bad. (Combat gets a bit repetitive, but the costume/character creator is a blast. )

For WoW, is it still a limited time trial?

No.

No, time isn't limited, it's just that you can't level beyond 20. And you can still make several characters per server.

DC Universe online, completely F2P with some features barred if you aren't a premium member, but they aren't to serious. It's also a newer game so it looks better than most others.

If you have Steam then there's also:

Spiral Knights
Realm of the Mad God
Iron Grip: Marauders
Puzzle Pirates

I can't vouch for a single one of them being good, as I haven't played them, but I guess you could check them out.