Forum Software

I'm a huge fan of BBpress. It's made by some people at Wordpress. I use to use phpBB but it was too big and clunky, and required way too many screens between surfing and signup.

BBpress is lightweight, highly configurable, and has a great and growing community. Love it.

Try looking on http://www.forum-software.org/ there is loads on there

I've used both and, although it's more expensive, I have to say that vB is much better. It's a lot more secure and has a lot more plugins available