Sorry that I'm late to the party, but there's one forum software that was not list - but it's the one that's gained my trust -- MyBB. :P
I currently use it for my Peach/Daisy fansite and the forums for my fangame headquarters site (if any of you are interested in more details on this front, PM me). :P
@ Bloc Partier: Yeah, I liked Lithiums forum software as well; too bad it only caters to businesses that have an interest in uniting their customer base. I'll have to admit, that's what "inspired" me to use MyBB's forum software since most operations are like Lithium's in a way. (I just had to borrow some forum icons from Lithium's system).