Great list, @WM7. Hope to see more like this one in future. I believe, that it took you a lot of time to put all popular forums together? Anyway, the job you have done for us here is perfect. Thanks a lot for it. Just would like to add another webmaster community, one of its king - BG and EN forum in Europe - http://www.predpriemach.com/ - more than 15 400 members and 460 354 posts. The forum is all about Internet marketing and has PR4, as well as Alexa rank 24 642. Created in 2006, now the forum combines 2 main languages - English and Bulgarian. Great place to get help and trade resources. It is the most popular one in its country and with the time (I hope) one of the most popular in Europe. The atmosphere there is friendly and everyone is ready to help you at any time and with everything. P.S: Sorry, that I get this thread up, I saw that the last post was on Mar 22, 2013. Well, hope you like the post.
webhelpforums.net may also be one - but of course sites like serverfault.com and stackoverflow.com are big now