BB Press is the 'standard' for WP installations. I've been hearing great things about the forum built into WP-symposium but I haven't had a chance to play around with it yet.
I have just installed it, works well but I don't know how to change theme. Everything is very nice but how can I manage admin c-panel. There's nothing moderators and all that.
If you want to install a forum along with wordpress then go with bbpress. One click installation of bbPress with this wordpress plugin: http://wordpress.org/extend/plugins/bbpress/
Simple press is a good option but bbPress is better because it is from the developers of WordPress, including Matt, so it integrates into your wordpress blog quite easily.
Forgot to mention that I've personally tested out this bbPress plugin on my Localhost wordpress 3.1.3 and wordpress 3.2 beta and it was working fine! Well I don't like to promote my blog this way but I've written a review and setup of this plugin. See here if you are interested: http://www.chasingeyes.com/one-click-installation-and-integration-of-bbpress-into-wordpress.html
This was a great thread. I was just about to come here and ask the same thing. Guess I am installing bbpress tonight.
Is the bbpess plugin new? Anyway to twist it to make a questions and answers forum and have use posts show in the category section? Or can this be done regularly with wordpress?
bbpress is good / best if you want to integrate a forum with wordpress! the plugin forum are not reliable ! If you want to host on sub domain seperately , than go for VB , if you can afford it !
i use a separate forum just to be safe and secure. mybb is better. although it can be integrated, i'd like it to be separated.