Baseball, especially the Sox. I will listen to the games on the radio, especially since I don't currently have cable to watch the games. I drive my family nuts!
In college, I was into the hockey. I went to UNH, which is a huge hockey school, and has had quite a few olympic players (including a few on the 1984 team). I keep wanting to go back to see them, but it hasn't happened yet.
As for a sport to play. I would say ultimate frisbee. But I have a hard time finding people that are interested in that one.