The first casualty when war comes is the truth.
 
Sen. Hiram Johnson
 
Morality is the best of all devices for leading mankind by the nose.
 
Friedrich Nietzsche - The Antichrist

Our World

Celestia

Celestia... Space simulation that lets you explore our universe in three dimensions.
Celestia runs on Windows, Linux, and Mac OS X.
http://www.shatters.net/celestia/
Downloads for each OS:
http://www.shatters.net/celestia/download.html
Addons:
http://www.celestiamotherlode.net/
A (not so) Brief Introduction to Celestia Addons:
http://www.lns.cornell.edu/~seb/celestia/addon-intro.html

WorldWind

Download it direct from NASA:
http://worldwind.arc.nasa.gov/