Well, PrisonTale is fun for a few hours, though it does get old - too much click-kill-click-kill to keep up the suspense, especially after you've done your quest at Lv20.
There's unofficial servers for lots of pay MMORPGs where the download is free, but I'm not going to say where (nor for that matter do I know where for most of them) since that'd be cheating

.
You could try Project Entropia, if you've got a credit card. They don't charge for playing the game; they charge for some services within the game (repairing weapons most notably), though I imagine if you were careful you could probably avoid needng to do that much, since I'm fairly sure you can pay with either real currency or in-game stuff; you'd better check that though.
Planeshift looks like it'll be utterly amazing with the next release. At the moment, its a nice looking 3D chatroom, though, and little else. But keep an eye on it, since their goal is to create a truly free MMORPG, so once the next ver is out, this'll be the one to play, I think.
Head over to
http://www.onrpg.com and have a look there; you might find what you're after...