OpenNetCF - Smart Device Framework
Heard about the OpenNetCF Smart Device Framework on Wally McClure's ASP.NET Podcast. It's a shared source framework that "enriches and extends the .NET Compact Framework by providing a rich set of classes and controls not available in the .NET Compact Framework."
Check out the library to see what's included, then download the latest binary and / or source here.
I just got an Audiovox SmartPhone last weekend, so I'm eager to see what sort of trouble this will help me get into.