Five days ago NASA dumped some photos onto a Flickr Commons account, at http://www.flickr.com/photos/nasacommons/:
So far only 180 photos. The Flickr blog says "Their Commons account will feature photos from across the agency’s many locations and centers, chronicling the history of space and lunar missions, and the people and places of the organization," so maybe they will be adding more.
NASA already shares lots of photos at http://nasaimages.org and of course the now like 90 years old APOD but the more limited, curated selection in the Flickr account makes it more approachable.
Curation is everything when it comes to disseminating media now; after Wikipedia was created it was proven maybe that just putting all the world's knowledge online improves how we get information but not how information gets to us. Curation is the new creation.