Really Digitalpoint and Sitepoint are the most active forums, SEO Chat has some knowledgable members as well but doesn't have the same amount of activity.
Agreed this one is pretty good as is sitepoint.com, both have alot of experts and alot of the same people are posting on both.
Here's a list of the top forums... Site Reference Digital Point SEO Chat SEO Roundtable Web WorkShop WebmasterWorld Forum Internet Business.co.uk Google WebMaster Help WebPro World SEO Guy SEO Refugee Cre8aSite Forum HighRankings Forum IHelpYou Forum Search Engine Watch Forums Now, I don't think that 'activity' is always the best sign as I find some have more knowledgable SEOs than others.... I'd rather have 3 quality discussions in a week than 20 useless ones... A signal to noise issue. And with any social platform, we gravitate to some peeps more than others, finding personalities U enjoy is also important. ..just sayin'
DP is more active than SP by thin margin... SP is more professional and big-time webmasters are there.. Here is the lists.. http://myseoblog.net/2008/05/11/list-of-dofollow-forums-with-dofollow-signatures/
No one has specified about http://www.warriorforum.com/Forum/ I know its a competitor for DP but a forum is a forum
If you really want to get real seo help and knowledge i would suggest you... ihelpyou.com/forums/ in this forum, there is no spamming allowed as much as spamming user does in most active forums. If one really want to discuss seo knowledge dan, Ihelpyou is the best destination.
I'd rather have less "activity" and more thought-filled knowledgeable answers such as SeoChat provides then have a forum full of activity but less knowledgeable members... Hey long time no see buddy... hows life been treating you?
Warriorforum is worst and admin and mods are unprofessional.. It has an advertisement in google against DP... I forgot the link here but here is the link from SP. http://www.sitepoint.com/forums/showthread.php?t=558020 Most members commented against WF, including me of course...