I'm a little new to Facebook, but everybody I know has been obsessed with Scrabulous lately. Scrabulous is an online game you can play with your Facebook friends that is similar to Scrabble. However, the nice thing is that you don't have to play in real-time. You put down your word and then wait until other players take their turns on their own time. This means that a game can last weeks or months, but at least you don't have to sit there getting bored while your friend freaks out over what he/she can do with three "Q"s.
If anybody wants to start a game with me, add me as a friend on Facebook!