"Atlas" Control Toolkit available for download
Here. Okay, yeah, it took a little longer than I'd hoped but we made some improvements in the meantime.
Check out all the details on the Atlas website, and we've created a forum for the toolkit as well. The controls in the toolkit are basically preview quality. They work at basic scenarios and we'll be releasing refreshes to deal with issues as we find them. But what's more important to me is that they'll hopefully give you examples to start writing controls of your own.
The toolkit includes full source for all of the controls, plus the sample website that demonstrates them. The source is licensed under the Microsoft Permissive License which allows you to modify and reuse the code as you see fit.
The toolkit also includes a VSI that sets up an "Atlas Control Project" template on your machine (VB and C# versions) that will help you get started writing your own controls.
In any case, start dreaming of the cool Atlas controls and extenders that you want to write and make it happen!