A fantastic world viewer program written in c# using managed DirectX. Read all about it here

Read about the decision to use Managed code and Managed DirectX here

WorldWind is on SourceForge. So if you want to look at source or help with an open source project go check it out

Worldwind was featured on .Net Rocks on 2/28/05. Listen to the audio here. The show features Chris Maxwell and Randy Kim who developed the application. If you want to skip right to the NASA stuff it starts around 11:50 in the stream.