I already love Baseball Reference, but now they've decided to broaden their horizons with a Wiki! Baseabll Reference Bullpen. If you're not familiar with the premise behind a wiki, it's a collaborative effort at something. In this case, a baseball encyclopedia.
It's still early, and there isn't much to read yet, but just give it some time and it will be awesome. Or, write your own articles to help the peeps out. It's a revolution up in here!