Resource Kits have some of the greatest tools for digging into a Microsoft product for fun, to learn more about the product, to support it better, or just to make your life easier. Here are a few that we find useful when building, running, and maintaining our demo. There are many more resource kits than just these though. Go to http://www.microsoft.com/TechNet to find others.
And see the list of MS Press Books for all the various Resource Kits