vBulletin is good (it's what the BODhost forum uses), but it is rather expensive. If you're willing to pay the license fee, though, then it's definitely a good choice.
phpBB is, some say, the leader in free forum software, but I disagree. Oh, sure, it's definitely popular, but I honestly don't like it all that much. phpBB3 is much better than previous versions, but the admin interface is still not very user-friendly in my opinion.
I would suggest you have a look at MyBB instead. It's
very similar to vBulletin and is almost as good, but unlike
vB, MyBB is free. Check it out, you might actually like it.
