The "Atlas" Control Toolkit is a set of nine great controls and extenders that use "Atlas" technologies and allow developers to easily improve the client experience on their websites.  All of the controls come with full source, and the toolkit also includes Visual Studio 2005 templates to get you started writing your own controls.

You can read more about the Atlas Control Toolkit over at http://atlas.asp.net/default.aspx?tabid=47&subtabid=477 and http://atlas.asp.net/atlastoolkit/.