Mingle Forum allows you to easily and quickly put a Forum on your Wordpress site/blog.

Mingle Forum Guest Info allows you to enable guest posts to Mingle Forum without registration while still collecting contributor's email info.

Simple to configure and nice looking forum plugin.

WP Bulletin Board (WPBB) is an easy to use forum for your Wordpress site with Facebook and Twitter features.

The Easiest WordPress Discussion Community Plugin. Effortlessly Build a Beautiful Community with Zero Coding, Seamless Embedding, Instant Setup, and Exceptional Support.