Ticket to Ride - a 2-5 player game where you connect train routes across the U.S. It takes 3 minutes to learn and is easy to play. There's plenty of room for strategy but enough luck that if you lose you can blame your bad "Ticket" cards. Heh. You can even play online at Days of Wonder
Lord of the Rings - This is a cooperative card/board game where you and your pals play the parts of Frodo, Sam et al and try to destroy the ring and whoop the pants off Sauron. It's cool because it's cooperative and it encourages working together and planning ahead. Of course when my buddy Drew and I played we had a horrifying run of bad luck and basically Sauron kicked our asses right away. It was as if during the opening credits of the movie you saw Sauron swallow up Frodo and Sam and then "The End". Still... I want to play again.