Check out the new "Atlas" Control Toolkit

Shawn and his team just released a set of Atlas controls that you might want to check out. It contains some useful controls and extenders such as TextBoxWatermark or ToggleButton (I really like how this one is implemented because it's really using an HTML checkbox despite appearances which is the right semantics and makes it really transparent to use). The controls come with full source code that the license enables you to modify and use as you wish.
http://atlas.asp.net/default.aspx?tabid=47&subtabid=477

Live examples are available so that you can check how the controls really work before you decide to use them.

The package also contains a toolkit that facilitates the creation of Atlas controls and extenders with some helper classes and templates:
http://atlas.asp.net/atlastoolkit/Walkthrough/CreatingNewExtender.aspx