As James Lau points out, version 3 of the Visual Studio 2005 SDK is now available. This is a significant release for several reasons which James enumerated:
The Visual Studio SDK contains a wealth of samples and tools for customizing virtually all aspects of the Visual Studio family of products, including Team Foundation Server.
It's also exciting to note that as of this release some of the licensing restrictions on the SDK have been eased. Specifically, you no longer need to register to download the SDK which means you can just download it from the Microsoft Download Center. You can also now (legally) use the SDK to extend Visual Studio to target non-Microsoft platforms as well, such as Java or Linux.