Maybe http://dribbble.com? I don't have an account, but it seems like that give you what you are looking for and have a niche group as well.

There's a lot of design forums but like dev forums, they can be pretty specialized.

Also, most of the best are private or invite only since ppl are looking for feedback or critiques for large clients.

Here's a few you could check out: http://www.qbn.com/ http://forum.howdesign.com/ http://www.designerstalk.com/forums/