Announcing "Atlas" Control Toolkit
Microsoft just released the first public version of the "Atlas" Control Toolkit. This package is a series of sample ControlExtenders that attach to existing controls to do some really cool stuff. My favorite is the TextboxWatermark.
It also includes Project and Item templates to help you build your own controls. It's a separate download from the main "Atlas" release, but I would assume that this would be rolled into the "Atlas" releases at some point.
Check it out!
UPDATE: Did I mention it comes with the complete source code? :)