http://moon.google.com/
"Welcome to Google Moon
In honor of the first manned Moon landing, which took place on July 20, 1969, we’ve added some NASA imagery to the Google Maps interface to help you pay your own visit to our celestial neighbor. Happy lunar surfing."
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Zoom all the way in and see what the moon is really made of.
Also available is
http://mars.google.com - while just as interesting it isn't as amusing. I guess they don't yet know for sure what Mars is made of.