I'm a bit late to the party, but here are my teams:
NFL: Cincinnati Bengals (AFC) and New York Giants (NFC). The Bengals are the team geographically closest to me, while my dad is a Giants fan.
MLB: New York Yankees (AL) and Cincinnati Reds (NL). The Reds are once again the team closest to me and I have had a few friends who like them too, and similarly to the Giants in the NFL, my mom loves the Yankees.
NBA: Don't follow the NBA as much as I do with other leagues, but I do have a soft spot for the Sacramento Kings even if they have struggled a lot in recent years. Probably because purple happens to be my favorite color.
NHL: Due to my family once again, I like the New York Rangers, but since I have a brother who is an Ohio State alum, we went to a few Columbus Blue Jackets games too and I happen to like them too (This was before realignment put them in the same division mind you).
MLS: Kind of like the NBA, I haven't gotten much of a chance to follow MLS closely, but I do like FC Cincinnati.
NCAA: I am a University of Cincinnati alum, so I can't go wrong with the Bearcats. I also like Ohio State for football since as I said before, my brother went to Ohio State.