Some fun writing forums...

http://writersinstitute.boardeducation.net/ (this one is run by Pen&Paper!)
www.writers.net
www.writingforums.org
http://www.eliteskills.com/forum/

I am a member on the first three forums. Just look for WaywithWords or Miranda Ashbourne.

Woots! I see mine! It's not all that fun yet, though...

Here are some nice forums that do forum roleplaying:

bb.surrealtwilight.com (the site that got me totally hooked onto it. It's the best!)

www.roleplayerguild.com

www.roleplaygateway.com

www.roleplayacademy.com (this one's special. It teaches people how to roleplay, but there isn't much to do if you're already good at it. It's affiliated with the previous site.)

z9.invisionfree.com/Roleplayers_Kingdom/index.php (yeah, it's really long, and you can't compromise on any part of the URL.)

I've got another to add to the list:

http://scribbles.forumotions.com/profile.forum

Here is the working link. Sorry about that.