NASA has an interesting application called World Wind 1.3 (not to be confused with Whirled Peas 3.1 - ed.). Using a 3D engine, the application utilizes high resolution satellite images to create maps that you can "fly" though.
The 180MB application's system requirements are: Windows 2000 and above, Pentium 3/AMD Athlon, 256MB RAM, 3D graphics card, broadband connection and 2GB of storage.
