It doesn't get much cooler than this. Visit Maestro Headquarters and "Explore Mars with the program that NASA scientists use to operate Spirit," the NASA probe that recently made a successful landing on Mars. You can follow the descent of the vehicle firsthand and view some of the first pictures from Mars, panning, zooming, and rotating images from the dataset NASA is using. I can't do this justice; download the Maestro application (>30MB download) and updated Mars data and try it for yourself.