I've been playing poker online at Paradise Poker. It's pretty fun, and you do not have to play for real money. I hang out at the play money tables. Most of the other free sites I've tried don't feel like a real poker game, because people are playing completely irrationally, with everyone calling or even raising with absolutely any trash hand. The free tables at Paradise are at least semi-rational, with most players aware of the existence of a Fold button.