LOTRO is probably the worst F2P MMO i've tried, its more like a demo than F2P.

Aion & Rift are decent, they pretty much give you everything at no cost and they offer very WoW-like experiences, if thats the type of MMO you're after. Dragons Prophet is decent too, i didnt play too much into it, but its quite different and from what i could see, you also have pretty much no limits as a F2P player.
KOTOR is a terrible MMO but a decent co-op game if you're looking to run through a story driven game with a friend, you can pretty much do everything as a free player in that too.

I'm currently playing a game called Vindictus, cant honestly say its a MMO, all of the actual combat is done in limited player number dungeons, but its really different from most of the other F2P stuff i've tried.