Here are some of those forums: Code: 4 http://www.go4expert.com/ 3 http://www.geekpoint.net/ 4 http://www.webmastershelp.com/ 3 http://www.webmasterforums.com/ 3 http://www.webmasterforums.net
I think it depends on what type of site you are trying to promote as well. The best thing is to find relevant blogs to post on!
I think that user's of the forums will be most interested if your site is relevant to there interests. Try searching in google for your site's keywords/primary topic plus the word "forum". You'll often find a few of the best forums for that niche very quickly. - Ben