Discovered this one last Christmas, and is probably my favorite board game of all-time:
Blokus
A hybrid of Tetris, chess, and Chinese Checkers, it is amazingly easy to play and very, very difficult to master. Every game is remarkably similar but dramatically different, and the layers of strategy will challenge almost any gamer. If you or someone you love enjoys board games, you'll love this one.
Some reviews:
Funagain.com
BoardGameGeek
Official Website