Baseball is easily my favorite sport.
In the majors I root for the Cincinnati Reds. They were World Champions in 1990, which may seem like a long time ago, but compared to the hell endured by Cubs fans, it's yesterday.
While I disagree with many of the things Major League Baseball has done in the last few decades (inter-league play, wildcards) they do have an excellent web presence.
Pictures and reviews of ballparks from around the continent at Ballpark Reviews.
The Brooklyn Cyclones, baseball in Brooklyn.
If into stats or history, check out the Society for American Baseball Research.