My NFL team is the Packers, and my MLB team is the St. Louis Cardinals. So yeah, I'm having a pretty good year.
I liked the Cowboys when I was very young, but kind of had an affinity for a few other teams... Green Bay was one, but also Houston (loved Earl Campbell). Then we moved to Wisconsin and I followed both the Packers and the Cowboys for awhile, but once Dallas turned into Jerry Jones / Miami Hurricanes west I threw them to the curb and stuck with GB. It helped when Favre came along and the Packers became respectable again.... in the 80s they were god awful.
I am a St. Louis Cardinals fan primarily because my father and his mother before me were.... they were dragged all over KMOX territory while my grandfather shuttled from Air Force base to Air Force base.
I follow the Flyers in hockey and have since the mid-80s.... it's a weird one as I've never lived remotely close to Philadelphia. I just decided that when I began watching hockey, I wanted somebody to beat Edmonton. So I picked the opponent they played in the finals that year, and it stuck. Plus I thought Pelle Lindbergh was bad a$$. Then he died, and I became attached to them. I like the Avalanche too and try to support them since they really are about a distant fourth behind everything else in Denver, but I never get that excited about them.
I am also a big fan of the Essendon Bombers in the Australian Football League. I spent some time in Melbourne and got absolutely hooked on the sport of Aussie Rules while I was there.... it became a great bonding mechanism between myself and my eventual in-laws when my relationship with their daughter got really serious.
As a kid I liked the 76ers in the NBA, because Julius Erving was my favorite player, although I haven't cared about basketball for years. The lockout doesn't bother me one bit.
Other college teams - I rooted for Wisconsin for a long time and considered them a second favorite. Obviously that has become enormously difficult. I now root for Turner Gill at Kansas, although that's not going so well.