Miravi 
I remember seeing Miravi posted on some news agregator site a few years ago when the European Space Agency started it. I had been working with Keyhole, which became Google Maps, at the time at what I believe is the now defunct Stevens Wireless Network Security Center. GPS devices were starting to become both small and cheap, and geotagging/geocoding was a nice way to demo mobility inherent in wireless comms.
Their satellite ENVISAT launched in 2002 and in 2006 they started making raw high resolution detailed images of earth available on their site. Over the years, they've racked up over 25000 images, all duly catalogued and browseable through a convenient interface that shows you on a world map roughly where an image lies. Their satellite mostly takes pictures worldwide, although the majority of them occur over the west coast of north america, brazil, europe, africa, south-east asia and australia.
There are a few things I find particularly interesting about browsing their collection. In the 3 years since MIRAVI has become available, we've learned to take satellite imagery for granted. It's been available for free in highly convenient, searchable form via Google Maps & Google Earth, Windows Live Maps, Yahoo! MAPS, and other web services. But these services offer a quilt of low-altitude fly-overs and satellite imagery, stitched together by computer to remove clouds. Often times boundaries between different shots show stark contrast in color or even resolution.
So I find it very interesting to view, for instance, a single continuous shot of the nile river complete with weather in the form of clouds, and conspicuously lacking any cartographic markings that saturate other online offerings. Looking at this picture you can understand what I learned about the Nile when I went to Egypt, and appreciate the scale of the Sahara and how it bears down on the life that clings closely to the river. You can appreciate the natural beauty of the earth and think about the history of the locations you are viewing and how they affected the people who lived there largely undisturbed by modern political boundary.
The only negative of the whole thing is the restrictive policy with respects to redistribution, which prohibit even derivative works. It would be an interesting project to use this wealth of data somehow, but unfortunately you could not share it without violating their terms of use. Hopefully someday they will allow independent people to use the data somehow.