For a while there was a really good group at http://www.digitalwebbing.com - that's where I've found most of the artists I've worked with. Good place to workshop art or writing, and look for collaborators.

But for a while, there was a weekly or bi-weekly tear-down session for comic scripts called The Proving Grounds, run by ComixTribe. They stopped doing it months ago. But I think there are years worth of posts still archived in the forum. I'd recommend checking it out.