I spend much of my spare time providing technical advice to folks on the web.
Microsoft.Public.WindowsXP.Network_Web is the Usenet forum where I started out researching first unsolveable network problem, and where I now give advice. It's a Usenet forum, that is also linked to Microsoft Newsgroups, and to Google Groups.
DSL Reports, aka BroadBand Reports, is a web forum which started out advising folks where to get Internet service in a given location. They have since expanded into technical advice of every imaginable category, and into non-technical advice too. For membership size, breadth of knowlege, and depth of knowlege, it's probably the most intense forum on the Web.
Google Blogger Help is a private Google web forum which provides technical assistance to folks with Blogger blogs. It's got 4 active subforums, each of which focus on specific topics in the Blogger world.
Googolians is a new web forum started by a fan of Google. Every Google product, and trend, is discussed here. It's small, but has promise.