Niceplot

I am using phpBB3 which is very good and easy to use, and can also be modified to do almost anything vBulletin can do.
Demo : free forums

I like PhpBB3. It has very few mods or themes at the moment, as it hasn't gotten a large enough community yet, but it's fast and easy to use. The admin panel is pretty easy, but gives lots of options. Since I'm too cheap to buy a script, I think PhpBB3 is close enough for what I'd need.

Demo: free forums

Invision Power Board definitely. A friendly community, more responsive developer community, tons of great graphics designers and modification developers, and more! Before my excuse for buying vBulletin over Invision Power Board was because it was cheaper, but now vBulletin is more expensive so it's better to just buy Invision Power Board. You get more. You have awesome support. It's cheaper!

Demo : free forums

Invision Power Board is a good one, it's also got a lot of free add-ons to add just about any feature you could want. but a Permanent License costs $130. ^^;;;

Demo : free forums

Invision Power Board.
Far more user friendly for admins and members. The developers put more thought in new features instead of just adding stuff. vB isn't very modern or modern looking unless you skin the hell out of it.
Demo : free forums

I use phpBB for my forums. I like the fact that it's open-source and the wide variety of mods and styles.
Demo : free forums

i prefer IPB. i have used it on many sites and find its a lot faster and easier to use overall. also most mods for vb are made from IPB mods. the major downside to IPB is the price if you actually pay for it.

Demo : free forums

I prefer phpBB because it has a very large community of users & developers who can provide support, it has a less restrictive license (GPL).

Also, with phpBB you can get "pre-modded" versions of the board (I've also seen a couple mods that include pre-modified files) which appear to be prohibited by the IPB license.

If you're looking for an easy installation, might I point out that surpass also has a phpBB installer in cPanel.
Demo : free forums

phpbb3 is probably the best free bulletin board. I am very pleased with it.
Demo : free forums

I definitely prefer PHPbb they have a bunch of add-ons and design templates that are also quite good.
Demo : free forums