Look at this image for a second. The main object is Phobos, the inner moon of Mars. But, look again. Do you see a faint smudge at the about 7 O'clock position? That is the planet Saturn!
Neat.
That whole set of images was awesome. But the fact that Saturn's ring system is evident in that particular image is really neat. Also the one with Jupiter where you can make out the cloud bands.