Established forum covering topics such as usability, Marketing and Promotion, Website Programming, Blogs, RSS and Syndication. Has an excellent website hospital where site owners can get detailed reviews. (highly recommended)
http://www.cre8asiteforums.com
Not strictly a forum but a blog where the best and worst discussions from all the popular forums are highlighted and discussed amongst professional SEO's. A massive time saver for those with forum addiction.
http://www.threadwatch.org/
A popular forum amongst SEO professionals which currently enjoys a great signal to noise ratio.
http://forums.searchenginewatch.com/
Long established forum covering all webmaster and SEO topics.
http://www.webmasterworld.com/
Web hosting discussion forum, used my many hosting companies, a great place to find a reliable host.
http://www.webhostingtalk.com/
Discussions mainly centre on Google and Link Building
http://www.webworkshop.net/seoforum/
Friendly forum covering SEO, marketing, hosting and other webmaster issues!
http://www.v7n.com/forums/
Topics covering all the major search engines and directories.
http://www.searchguild.com/
Ask for help with topics such as site design, site programming, web hosting, site promotion and running an online business
http://www.sitepoint.com/forums/
Offers discussions on a variety of SEO/SEM topics including keyword research and marketing.
http://www.highrankings.com/forum/
Open discussion about anything related to search engines and search engine marketing.
http://www.seo-guy.com/forum/
Discussion related to search engines, including optimization, marketing, tools and other technical aspects.
http://forums.digitalpoint.com/
Business and marketing forums with search engine optimisaton news and workshops.
http://www.platinax.co.uk/forum/
See what the evil black hats are up to, but be careful you don't turn to the dark side.
http://syndk8.net/forum/index.php