my.opera.com/community/forums/ htmlforums.com/ kirupa.com/forum/ newgrounds.com/bbs/ pixelex.com/ sitepoint.com/forums/ v7n.com/forums/ ozzu.com/ phpbb.com/community/ webmasterworld.com/
NetGum is a new forum. it has free blogs and is good for a free backlink at least since it is at an early stage.
dp is my dearest forum though, but i use build.reciprocal, webmaster-talk, searchenginewatchforum, namepros, webmasterworld, articlestar, .
I used to be very active at webmaster-talk.com, I think the Mods there are easy, but they keep the forum runs. I found DP is a more active forum, good for getting backlinks, many be people spam alot on DP, but still it's a good forum.
Mainly here in DP if I have any recreational time http://www.advancedphysics.org/forum It's resource helps me to comment on .edu sites and with engineering problems for one of my design prototypes ROOFIS