This link has been available for quite a while, but I never posted it in my blog. It's easy to get overwhelmed trying to keep up with extensions available for Visual Studio.
One central place where we list a number of useful extensions for Visual Studio is Defy All Challenges. You can find Office development tools, .NET 3.0 tools, AJAX tools, and Team System tools listed there. It's not comprehensive, but it's a good baseline set of extensions.