I've been researching a project which invoved collecting urls of SEO forums and bulletin boards. Although not strictly a list of pure SEO forums, it has a lot of meaty search engine marketing conversations going on.
I'm interested to know how many forums people are signed up to?
Webmasterworld PR 8
SEO Chat PR 7
V7n PR 7
Digitalpoint PR 7
Searchenginewatch PR 7
Cre8asiteforums PR 6
Submit Express PR 6
SEOguy PR 6
Highrankings PR 6
Searchguild PR 6
Searchengineforums PR 6
Webmaster-corner PR 6
htmlcenter PR 6
SEOrefugee PR 5
Seoblackhat PR 5
Syndk8 PR 5
Webworkshop PR 5
SEOforum.org.uk PR 5
Ihelpyou PR 5
FathomseoPR 5
seo2020 PR 4
SEOforum.us PR 4
Sitepoint PR 4
Selfseo PR 4
vasuinfotech PR 4
AOSEP PR 4
Mr-seo.com PR 4
Revenueresource PR 4
David Castle PR 3
Top25web PR 3
Marketing Chat PR 3
MKpitstop PR 1
David Castle PR 3
seo1 PR 0
They are ranked in order of PR as it's the quickest way to get a rough layout of the most and least popular. This does not mean better, it simply means more PR. Read into that what you will.