I support my local American team, Philadelphia Union (yes, we have a soccer league, and one that is actually quite good, too) and Liverpool FC. Both teams are currently trying my patience with awful seasons, though it looks like Liverpool might be turning things around.
Also follow the USA national team. I can't complain with most of the results Jurgen Klinsmann has been getting us (beating Italy and Mexico on their own turf for first time, etc), but some of his personnel and game-day choices are absolutely maddening and seem to defy logic. I also follow the women's national team, though that's probably because they're waaaaaaay better than the men's, and most of the players are really attractive.
So yeah, soccer is pretty much my religion.