If I were running the space program—which is unlikely, I admit—Saturn's moon Titan would be very high on the list of destinations for the next major planetary mission. Sure, Mars is appealing, largely because of its similarity to Earth.
But take a look at this radar image of Titan's northern polar region, returned by the radar instrument on the Cassini orbiter. Seem familiar? The only other place you'll find features like this—flowing rivers and lakes still filled with liquid—is Earth.
This is Titan, though, where the temperature is 290 degrees below zero. So the liquids are likely to be methane or ethane, not water. The "lava" oozing from Titan's ice volcanoes is made of water and ammonia, and is as thick as taffy. It rains there, sometimes heavily, and there may even be fog. All of which makes this place Earthlike and utterly alien at the same time—the perfect target for exploration.
The vehicles proposed for studying Titan are as fun as they are varied: rovers, balloons, airplanes, even boats. And there's a real chance of finding life, or at least its precursors, on a moon with more organic molecules than any other place beside Earth, and transient liquid water on the surface.
Let's hope that NASA and the European Space Agency heed a recent recommendation from planetary scientists to send a large "flagship" mission to Titan in the 2020s, and perhaps a small probe even earlier.