Abakus Forums - SEO forums - smaller, but they have a larger German version too. Webby moderates at a good number of various SEO forums. Swell chap
Anthony Parsons SEO Forum - Ran by ... Anthony Parsons. It is still rather quiet as I do not think he has promoted his forum much, but Anthony makes many thoughtful posts at many other SEO forums.
AOSEP - newer smallish SEO forum started by some Searchguild moderators.
Band of Gonzo's Webmasters Forums - A few of the lead posters at WebProWorld created their own SEO forums. Dodger tends to dig up a good number of interesting news pieces.
Cre8asite Forums - usability / design / webmaster forums - mid sized. Guys Like Peter D, Black Knight, and bragadocchio post many enlightening posts with lots of experience in business and marketing.
Digital Point Forums - Shawn Hogan's mid sized SEO forum. Shawn is a programmer by trade and has created some of the coolest free SEO tools available. His forums tend to be rather liberal and many people who are kicked out of other SEO forums learn now to behave before they get kicked out of his (I do not think I have ever seen him ban anyone). He seems like a rather swell chap.
Highrankings SEO Forums - Jill Whalen's mid sized SEO forums. Jill is branded as "the SEO copywriter." Her forum is geared primarily at people new to SEO, but there are also a variety of more experienced SEOs there too. Her forum tends to be rather conservative or "white hat."
IhelpYou Forums - Doug Heil's mid sized SEO forums. Doug is a self appointed crusader against search engine spam. He is quick to judge and his opinion is strongly reflected in his forums. Above when I wrote about the gossip column posts at ThreadWatch the one about Doug Heil's SPAM comes to mind.
Jimworld - large webmaster forums. A bit past its prime in my opinion. A larger and older forum on the forum scene which I rarely visit.
LilEngine Forums - smaller SEO forums. There is not much activity at LilEngine. When I first started moderating there many people did tons of link drops, but I have been trying to delete them out as best I can.
Ozzu - mid sized webmaster forums. I do not post at their forum frequently enough to adequately review it, except to say that it has a decent signal to noise ratio and a cool looking design
Resource Zone - Webmaster forums for public interfacing with the DMOZ (Open Directory Project) editors. Lots of major webmaster conflicts occur there. Some of the editors are great, but some are also judgemental and mean. Often frustrated webmasters directly accessing these editors means you get to see the best and worst the editors have to offer.
Search Engine Watch Forums - newer SEO forums where many long time SEOs hang out. One of my favorite SEO forums.
SEO Chat large SEO forums. The signal there is kinda drowned out by tons link drops and some of the top SEOs are driven away by the massive amounts of advertising on that forum.
SEO-Forums.com - James Mann's small new SEO forums. I have not visited it enough to give it any sort of review...I can only state that it is kinda small and somewhat new.
SEO Guy Forums - newer SEO forum which has taken off well. SEO Guy is a longtime member of SEO Chat. When he made his own forums many of SEO Chat's best members went with him.
SEO Town - Darrin Ward's new small SEO forum. After his 1 year non competing clause with SEO Chat lapsed he made the site, but it has not really picked up much steam.
SEO Talk - Newer small SEO forum from the people of Webmaster Talk.
SEO Zip - Nandini Maheshwari's newer SEO forums. I help her moderate there.
SearchGuild - Chris Riding's mid sized SEO Forums. One of my favorite forums. Great signal to noise ratio and great sense of community.
Top25Web - Anthony Ettinger's small SEO forums. He is a programmer by trade, and I believe the Top25Web forums are primarily geared toward those new to SEO.
V7N Web Dev Community - mid sized webmaster forums - John Scott's SEO forums. John has a tendancy to be blunt, but he means well. I post there frequently.