Subcategories:
Forum Directories 
1. 1001Forums
A large message boards and forum directory. Helps locate web communities for talk with other people about the subjects in common.
http://www.1001forums.com/
Directory and search for select online forums.
http://www.directoryforums.com/
Search for, rate, and review discussion forums and message boards in a human-edited directory.
http://www.findyourforum.com/
Directory of internet forums, discussion boards, BBS, and message boards in which global and local forums are sorted by subject and country. Ranks top forums and message boards on the basis of viewers vote.
http://www.forumdirectory.biz/
Directory of forum directories with listings of forum only directories and forum specific resources. A great link building resource for all forum owners.
http://www.forum-directories.com/
A directory of forum sites based on the Invision Power Board platform.
http://www.ipbdirectory.com/
A comprehensive listing of PhpBB forum sites. This is a great link-building resource for PhpBB forum owners.
http://www.phpbbdirectory.com/
A comprehesive list of Vbulletin forum sites. A great link building resource for all vBulletin forum owners.
http://www.vbulletindirectory.com/