I second the guy who said Aion, it's a very solid MMO, probably because it used to be P2P, and is honestly the only one I can think that didn't cut content when they went F2P (as in limiting races or classes, or quest lines that were available to all players originally but only to P2P afterwards with options to buy for F2P). Well, maybe Archlord but I don't know if that's still around.
I'd also recommend the two superhero games out, DC Universe Online and Champions Online, if only because the combat will feel different from a standard MMO.
I'd also recommend the two superhero games out, DC Universe Online and Champions Online, if only because the combat will feel different from a standard MMO.