If you're just getting started promoting you forum and pulling you hair out trying to figure out how to fill up the categories with quality posts and threads so that visitors feel comfortable enough to drop a few posts of their own, then you should probably know that there are services out there that support this practice. While marketers could go around and around about the ethics of hiring paid forum posters, it definitely happens. Here are a few services you might want to look into to get your own forum off the ground or back to life.

ForumBooster.net Pricing ranges from $22.99 (for 75+ posts, 25+ threads and 2-4 registered users) to $149.99 (700+ posts, 70+ threads and 7-10 registered users).
PostingDirect.com A little confused on the pricing. $139 for the service, but now available for just $39. There is no information or guarantees on how many posts will be made but I will say that you can usually trust a guy that puts his real phone number on the site.
Forum-Posting.info Pricing is similar to that of forum booster but this service ranges up to 2,000 posts, 250 threads and 150 users for just under $300. Interested parties can even sample the service with a special trial offer of 10 posts for $4.95.
ForumWizards.com Certainly one of the least descriptive sites I've come across but the rates are the most reasonsable. A sample package (10 posts, 2 threads) starts at $2 and the full-on Monster package runs just $90 for 11 users, 500 posts and 100 threads.
ForumAdvantage.com Well priced tester package (7 posts, 3 threads) for just $5. A wide variety of packages all the way up to the Total Package for $525 that includes 1,500 posts and 500 threads, 8-16 users).