Pro football - my father grew up in the Florida panhandle, so some of my earliest memories are watching with him the classic Griese and Czonka teams of the mid-70s. Thus I grew up a Dolphins fan. I actually do recall rooting for the Colts in the 1971 Super Bowl against Dallas, just because they had white jerseys, and when the Colts moved to Indy in the 80s I became a fan since I lived in Indiana the first 15 years of my life. Then when the Titans moved to Tennessee I started following them a bit also. And of course, I am partial to the Broncs so long as Peyton is there, and that is really recent.
Basketball - Pacers fan from the mid 70s. Always have been, always will be. I like the Clippers to an extent, because they are NOT the Lakers.
I almost moved to LA in 2001 and if I had I was planning to wear Clippers gear all the time and announce loudly that I would NOT want to be seen on the sideline of Lakers games and that Jack Nicholson can kiss my ass anyway.
Baseball - grew up a Reds fan and still follow them a bit. Not a huge baseball fan though, so basically I just check the standings every now and then, but haven't even really been doing that lately.
College football - Huge Vol fan though I evolved into it. Was a casual fan upon moving to Knoxville in 1982, then became a real fan upon enrollment in 1985, but still had divided loyalties because I was a huge Notre Dame fan starting in 1977.
Switched loyalty completely to Tennessee in the 1991 "miracle in South Bend" because I didn't like the announcers dissing Tennessee. Nowadays Purdue has replaced ND as no. 2 since I got a grad degree from Purdue.
Hockey - used to like the Indy Whalers of the old WHL, but they are long gone. I only watch hockey during the Olympics, but if I had to pick a team it would be the Preds for obvious reasons.