Developed by NASA, World Wind is a program that renders (creates) a 3-D model of the earth, A virtual globe that you are able to turn, shift, rotate and more. World Wind does this with incredible precision, providing a myriad of options, plug-ins, and tools that can be used for any number of purposes. The list of futures just goes on and on, it’s really quite something and, as I said before, the program surprised me with it’s capabilities and polish. Here’s a list of the features that you can read about on the Features page. I believe that most of you will be impressed: 3D engine, Blue Marble, Land Sat 7, SRTM , Animated Earth , MODIS , GLOBE , Country & State Borders , Place Names , Visual Tools , Landmark set.
http://worldwind.arc.nasa.gov/features.html

This program is free, but its also a beast. It requires Windows 2000 or XP and the hardware requirements are:

• 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

But, if your PC can handle it, this program is incredible. You can zip all over the globe and get satellite imagery. Its a lot of fun.