Maybe <a href="http://dribbble.com" rel="nofollow">http://dribbble.com</a>? 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.<p>Also, most of the best are private or invite only since ppl are looking for feedback or critiques for large clients.<p>Here's a few you could check out:
<a href="http://www.qbn.com/" rel="nofollow">http://www.qbn.com/</a>
<a href="http://forum.howdesign.com/" rel="nofollow">http://forum.howdesign.com/</a>
<a href="http://www.designerstalk.com/forums/" rel="nofollow">http://www.designerstalk.com/forums/</a>