Chris Craft has done a great job in getting a lot of people excited over using .NET for Mobile Applications. He has created a new application each day for 30 days. Some of these are not too complicated, but they are all very cool. With some going way beyond what you would expect for such a short period of time.
My favorites are:
You can check out these and all of the other applications he has created on his blog. The great thing about these programs, is that he includes the source code as well ! Enjoy.