Best. Space probe. EVER.

Well, OK, Voyager was right up there. And Galileo. And the Viking landers were pretty cool. OK, all the space probes are unbelievably cool...but I really heart Cassini, which took this image of the Saturnine moon Dione:

Those skinny things at the bottom are Saturn's rings, viewed edge-on. Wow. My opinion of the space shuttle and the International Space Station aside, the part of our space program that uses unmanned ships to do good science would be a bargain at twice the price.

(Embiggened version of this image, with informatory material, here. Link via Paul Riddell.)