Sailing the planets
Floating just several kilometers above the surface of Mars, the guided Mars balloons can observe rock formations, layerings in canyon walls and polar caps, and other features - at very high resolution using relatively small cameras.
The Mars-balloon idea has been making the rounds for year; perhaps the success of the rovers will spur someone -- such as the European Space Agency -- to finally go for it. Imagine one of these automated jellyfish hovering over the Face or dipping its guide-ropes into Valles Marineris.
(There's always the risk of getting snagged on one of Arthur C. Clarke's "banyan trees," but I think it would be worth the sacrifice.)