Another vote for WetCanvas. That's the forum where I learned how to become a self-representing artist: how to conduct business online, how to blog, how to stage a real-world show, and a thousand other things.
I consider WC to be my art business University. My favorite WC channels are The Art Business Center, and Internet Sales Strategies.
I'm 'EyeSpy' over there -- it was my very first art forum, and I've never switched to my 'other' (but not secret!) identity. ;-)