phpBB

phpBB is a high powered, fully scalable, and highly customizable Open Source bulletin board package. phpBB has a user-friendly interface, simple and straightforward administration panel, and helpful FAQ. Based on the powerful PHP server language and your choice of MySQL, MS-SQL, PostgreSQL or Access/ODBC database servers, phpBB is the ideal free community solution for all web sites.
http://www.phpbb.com/

  Forumcities

Offering free message boards for webmasters. Includes options to ban IP addresses or HTML postings. Also includes a neat ICQ feature that allows you to chat with other members of the board in real time.
http://www.forumcities.com/

  Discus

A free WWW discussion board software package that can be installed on a Unix, Windows 95/98, or Windows NT web server.  Over 3000 internet sites are using Discus.
http://www.chem.hope.edu/discus/

  ezboard

Offers free, easy-to-use, Web-based message boards that engage both businesses and consumers to create and participate in completely customizable and personalized online communities, which may be seamlessly integrated with any web page.  ezboard is fast, free, and easy!
http://www.ezboard.com/

  Beseen's Bulletin Board

Build a sense of community between you and your customers, allowing your visitors to interact with you, your staff and each other by posting questions and comments.  No programming required. Easy setup and simple to maintain.
http://www.beseen.com/board/index.html

  CommunityApps from server.com

Provides full-featured, group message board functionality for your web site. Unlike other web forums, the messages don't expire after a month, and we don't try to drag your users away to other forums.
http://www.server.com/communityapps/discussionapp/index.html

  Amazing Forums

Create message boards for your Web site with powerful custom options such as user banning, foul language remover, html remover, editing, email notification and color customizing the message board.
http://amazingforums.com/