There's two LJ art communities sorely in need of more members as their participation is really low.

First off is the Sketch exchange found here:

http://community.livejournal.com/sketch_xchange/

It's a really fun community and sign ups for the April round starts tomorrow so go ahead and join so you can take part.

Second is one I just joined last month called dragon_exchange. If you are a dragon artist and have time to draw at least one polished dragon picture a month, you should give this community a try and sign ups for their next round should be starting up soon.

http://community.livejournal.com/dragon_exchange/