MozillaZine forums

I also find newsgroups very useful. Almost anybody can set up a web based forum, so there are often dozens of web forums on a particular topic that don't get much traffic. But very few run their own news server, so there isn't as much overlap. The downside is that they usually purge old messages on a regular basis. (And no avatars. Sad)

The Dreamweaver newsgroup on forums.macromedia.com is a good place to ask questions on CSS & HTML.

gmane.org is another useful resource. They run a news server that allows you to read and  post to many open source mailing lists using a news reader. They also do not purge old messages, so it acts as an archive.

Of course Microsoft's news server (news.microsoft.com) is a good resource on Windows topics.