One of the powerful features of Visual Studio is the extensibility model it provides that enable advanced developers to extend and enhance the built-in product. Using this you can build wizards, menus, integrate with the text-editor, etc, etc. The current build of the VS 2005 Web Application Project (which introduces an entirely new web project system) is actually built entirely using these public APIs.
Today the Visual Studio team published a set of samples that shows how to use these APIs. You can download them here.
Hope this helps,
P.S. If you haven't read James Avery's article on "Ten Must-Have Tools Every Developer Should Download Now" you can check it out here. It includes some great add-ins (some built with the above APIs, some not) that you can download and use today.