Glaciers and Volcanos on Mars
The European Space Agency has some great pictures of the North Pole of Mars, taken by the Mars Express probe. It appears that there may be some active volcanos on Mars.
I am philosophically supportive of manned space exploration, but this sort of result, like those of NASA's Mars Exploration Program rovers Spirit and Opportunity, makes the case for doing as much as possible by robots before risking the lives of humans.
Then, there's the spectacular success of the Cassini-Huygens mission to Titan, a place we are not likely to ever send people.
There are people of all political stripes that think that this sort of thing is a waste of money. I disagree, and would argue that it stretches both our technical abilities and our conceptions of ourselves to explore in this way. If I have a complaint, it's that these results, and what they imply, aren't getting more media attention.