sitepoint.com is one and you can find many forums like dp by searching in google,but you can't find more traffic than dp .
A few that i'm a part of: www.seobum.com www.webtalkforums.com www.decentdiscussions.com Some that I really should join sometime: www.sitepoint.com www.ukwebmasterworld.com
I hear that WebMastersHelp.com has the best admin ever. And the forum at SEO.com has several very cool admins.
I also know another website started recently. Its vuju.com The best part of website is that we can chat with vuju owner whenever we want, and he hears to all our suggestions.
Yeah, I noticed that you are a member there, or at least someone signed up with the same user ID. You should come by and check it out. The forum has grown a bit.
I signed up there long back just a month after I joined DP have a few posts but DP is so addictive that I dont feel like going to any other forum :|
A friend just opened a new forum that looks promising. It would be cool to be a charter member. Who knows, it could be the next greatest forum for webmasters! http://webicero.com/
Wickedfire.com is another one, but unfortunately you have to be a ho-mo-sexual to go there and view a initiation video...Very sad, it's a great place with lots of information.