Here's a nice list of .NET CF (Compact Framework) projects you can play with. The first three items (FotoVision, TaskVision and Signature) make good demos. These are all courtesy of Vertigo Software.
Scott Hanselman is a former professor, former Chief Architect in finance, now speaker, consultant, father, diabetic, and Microsoft employee. I am a failed stand-up comic, a cornrower, and a book author.
Disclaimer: The opinions expressed herein are my own personal opinions and do not represent my employer's view in any way.