Probably Dungeons & Dragons Online, the Turbine MMO. I find that I am able to play the game with friends who don't sub and they can truly play a LOT of game content for free.aescuder said:I'm currently playing Spiral Knights, a free-to-play MMORPG, in steam right now.
It's the same company that does Lord of the Rings Online and Turbine is known for doing the F2P model well.