Well, I occassionally play Saga of Ryzom online, but only because there's no offline mode. I'll probably stop doing that once the fees kick in.
There don't seem to be any really interesting online games on the market right now, all you can get are FPS and RTS games. In the former you get killed by people who don't have such a f###ing high ping, in the latter you have to learn build orders by heart unless you want to lose in five minutes. Then there are the racing games, which you lose if you make a single error... Oh, of course there are the click&watch... err.... MMO games but aside from Guild Wars they all cost money to play.