My little brother started me on this board game he has called BLOKUS. It's like tetris pieces, sort of, and it's a competitive multiplayer puzzle thing.
And you can play the original game and all variations of it (# of players, shape of board, etc) for free.http://www.blokus.fr/online-game/
Make an account (free) if you want to keep identity, or just hit "Guest" for quick games.
If you've never played this before, it is HIGHLY addicting. Watch out! I'm a big fan, and was "converted" in about 2 weeks. :)