Google Mars
http://www.google.com/mars/

"...Those map-happy souls at Google announced today the launch of Google
Mars, built by the scientists at Arizona State University's Mars Space
Flight Facility from over 17,000 images. It shows quite a lot of the
Martian surface in visible-spectrum, infrared and elevation views. A few
particular features, such as the fascinating Olympic Mons volcano and the
two Rover landing sites, are mapped in extensive detail..."