Participating in forums can contribute great to a SEO campaign both with backlinks from signatures and mainly with knowledge about latest trends in online advertising and promotion.
I decided to share my list of top Webmaster, Search Engine Optimization, Blogging or related forums. Here it is:
http://forums.digitalpoint.com/ - Great forum with a lot of information for search engines, marketing, business, design, development and more.
http://www.v7n.com/forums/index.php also great forum.
http://www.webcosmoforums.com/ - promising forum
SEO centered forums
http://forum.abestweb.com/ - affiliate centered forum, great knowledge for making money online
Blogging centered forums
http://www.bloggeries.com/forum/ - my favorite blogging forum