I enjoyed using play money on party poker -- they have some funky spyware they drop in your machine with the download though.
I've enjoyed using Full Tilt for a while now. I agree that the experience of seeing lots of hands play out is helpful. There are plenty of ass clowns that go all in and chase like a bunch of mo-fo's, but I do feel I've gotten better just by seeing a bunch of hands, experimenting with varying degrees of aggression, etc.
