I've held off from nominating my site, but I nominate Strike 3 Forums. Since nominations must be in by the end of the month, this is a bit early, but with it being October we have a lot of different things planned for the playoffs, so our activity and content should be rocking by the end of the month. As far as what seperates us, we really try to be ahead on the curve in terms of what other baseball forums do (in terms of content, physical appearance, extras such as Out Of The Park sim leagues, among others), I like to believe we have a pretty unique visual identity, a casual community where it's really easy to get to know everyone and we're very clear about what our passion is.
http://strike3forums.com/forums/
Anywho, I second myetalk (
http://forums.myetalk.com/index.php/).