NHL: San Jose Sharks. And if I had to give up all other sports just so I could keep watching them, I would. I had season tix their first seven seasons before moving to the land of the most spoiled fans in all the NHL.
NFL: St. Louis Rams. Rooted for them since childhood, suffered through the 80's and 90's surrounded by evil Forty-Niner fans; it wasn't pretty. (AFC I guess I root for the Broncos - Jake Plummer went to my high school and I live 60 miles from Denver.)
MLB: Rockies. Whatever.
NBA: I still root for the Lakers of the 80's. I have no use for the NBA these days.
College: Colorado State University Rams. Local team. I went to San Francisco State - I didn't even know we had a football team until a couple weeks before I graduated. (fyi - they've since disbanded the program. )
Horseracing: Any horse ridden by Gary Stevens, who was in my graduating class in high school. He's won the Kentucky Derby three times. Those of you that don't follow racing but saw "Seabiscuit" will know him as jockey George Woolf.