I used to be a Barcelona fan, because of the Dutch connection they had with Cruyff and several dutch players, and I saw a game in their stadium with a couple of dutchies, but its hard to like a club that is winning soooo much that it gets boring.
Football: Manchester United (former season ticket holder for many seasons, prior to the Glazers takeover and moving to London)
American Football: Miami Dolphins
I also have a soft spot for certain other football teams across Europe, mainly based on some of the great players who played for them during my childhood.