Google Earth and NASA have completed their project for a NASA layer in Google Earth. This was initiated in an effort to raise awareness and promote NASA's earth programs.
The new NASA layer has astronaut photography of Earth, satellite imagery, and earth city lights. Incorporating photos and images that NASA has been collecting for decades, the astronaut photography of Earth really showcases some great stuff. The satellite imagery has some options for downloading images in order to overlay them on the earth's surface, offering some manipulation options that weren't available prior to this collaborative project. Earth City lights is another interesting option for viewers, and these new tools and images will surely bring about some interesting map mashups.
See also: 13 Must-See Google Maps Mashups