Cassini flies by Tethys and Hyperion, and the photos so far have been awesome and weird! I especially want to point out this fascinating view, which, if you look at it closely, reveals what appears to be a string of small impact craters, in a straight line over older terrain. What kind of meteor impact could have produced such an excellent formation of craters?
Update: On Metafilter, freedryk mentions Shoemaker-Levy 9, the comet that broke up as it crashed into Jupiter in a series of linear impacts. Similar forces may have been at work in the line-of-craters on Tethys.
Update: Hyperion photos are coming in.