Postloop | Content Marketplace
It's basically the best post exchange program I've come across and it'll bring you quality content only. You're gonna have to review people posting on your forum and give them a rating, so they'll have to make sure they post quality messages. No garbage one-liners.
Taken from their FAQ:
What is Postloop? Postloop is a marketplace and exchange for Forum Owners, Blog Owners, and Content Writers. Forum owners can use Postloop to attract more posts to their forums, blog owners use Postloop to attract more comments to their blogs, and content writers use Postloop to earn money for posting in forums and commenting on blogs. All of the exchanging of posts and comments is tracked automatically thanks to Postloop's exclusive monitoring service. It tracks activity in real time and automatically matches up forums and blogs to writers so that Postloop users do not need to bother setting up their own contracts and agreements.I've heard that quite a few people are able to actually earn money out of it, which is interesting.
If you ever need a hand with your forum, head to www.postloop.com and experience it yourself. It works!