Anyone tried WorldWind?
Features:
World Wind lets you zoom from satellite altitude into any place on Earth. Leveraging Landsat satellite imagery and Shuttle Radar Topography Mission data, World Wind lets you experience Earth terrain in visually rich 3D, just as if you were really there.

Virtually visit any place in the world. Look across the Andes, into the Grand Canyon, over the Alps, or along the African Sahara.

Not really nice on the requirements though:
Windows 95, 98, ME, 2000, or XP
Intel Pentium 3, 1 GHz, or AMD Athlon or higher
256 MB of RAM
3D Graphics Card
nVidia GeForce 2 Ultra
ATI Radeon 7500
Intel Extreme Graphics 2
DSL / Cable connection or faster
2 GB of disk space

Source:http://worldwind.arc.nasa.gov/