Free or commercial forum software? And do you just want forums or do you want a suite with gallery, blogs, etc.?
1. Xenforo 2. Vbulletin The rest don't matter. For free I'd say MyBB is the best, but I don't like working with free scripts anymore.
Xenforo is my favorite right now, as it's got some really awesome features, even though it's lacking a few resources. Also, mybb and phpbb are good examples of free solutions for a forum community