Earth
Earth Impact Effects Program - This program will estimate the seismic, blast wave, and thermal effects of an impact as well as the size of the crater produced by the impact. The crater size is determined using pi-scaling. (86 visits)
http://www.lpl.arizona.edu/impacteffects/
Google Earth - "Explore, Search and Discover" (51 visits)
http://earth.google.com/
The Size Of Our World - (44 visits)
http://www.rense.com/general72/size.htm