Adding and building a forum for your website is a great way to build additional website traffic. Forums are indexed in Google and allow for other people to have conversations right on your blog. These conversations get indexed by Google, linked to by other webpages, and build more content for your website. This all leads to one think you are trying to get more of, traffic.
I chose to stick with BBPress for my forums. BBPress is essentially from the makers of Wordpress, is free, and can easily be linked to your Wordpress blog, even automatically importing all the user names and passwords from your Wordpress blog.
A popular chose for building a forum is also VBulletin which would set you back $180. It isn’t that much though if you want a really good forum. Plus VBulletin has a lot of support. Still in the end I chose the free solution since I can always upgrade later.