NASA World Wind
This is great! Thanks to Steve Makofsky for pointing it out.
In a nutshell, it allows you to zoom from any satellite altitude into any place on earth using various images captured from LandSat and STRM (Shuttle Radar Topography Mission) elevation data. It's pretty impressive and definitely worth the 231MB download (although, it requires some pretty beefy processing and video power).
Pretty cool that it's written in .NET.