You are probably getting ready to see all sorts of blogs posts on this because frankly, Photosynth is very very cool.
Photosynth uses hundreds of standard digital camera images to construct a three-dimensional view of an environment or "synth". These synths can be explored much like a video game, allowing you to explore, zoom into tiny details, and see where the photographer was standing (or flying) when they took the pictures.
Now that you know what is is, head on over to http://spaceworld.msnbc.com to see the NASA collections.
Current NASA collections include:
For some background on this project, see the video at http://media.labs.live.com/photosynth/NASA/videonasa.html or the collections at http://media.labs.live.com/photosynth/NASA/CollectionHome.htm. See other Phtotosynth collections at http://labs.live.com/photosynth/collectionHome.htm.