There's been a thread going around internally about this really cool application written in C# on .NET: NASA's World Wind. World Wind is a kind of geographic information system (GIS) application that lets you view satellite and shuttle images of the world, including the "blue marble" picture of a cloudless Earth and 3D renderings based on shuttle radar topography images. Aside from the fact that the images are just visually stunning and the application and data are free, what I found particularly interesting was Chris Maxwell's (World Wind's lead developer) explanation of why he chose C# and DirectX. The classic quote for me was: "This productivity issue comes into play when it's just one guy (a student intern) programming the entire project. Going the C# route was the difference between finishing the project, and not finishing the project."