I don't normally like posting a link to whatever all the news sites are posting to, but NASA'S World Wind is stunning and I need more RAM.
The Instructions tells you how to get the panning thing working so you can see the world in 3D, but this is the first proper application that I have seen that uses Managed Direct3D. All programs will be written in Managed code in two years, but it is interesting to see NASA take a lead with such an interesting program.
The coolest feature is the Scientific Visualisation Viewer which allows you to watch events like a forest fire or flood from a satellite viewpoint.