Lakes

Cassini, the spacecraft currently observing Saturn, its rings and moons, has been mapping the polar regions of Titan, a large moon with a dense methane-rich atmosphere. Large hydrocarbon lakes make up about 14% of the polar surface, some larger than the midwest Great Lakes. The lakes are theorized to have formed similarly to Earth's lakes, and indeed much of Titan's structure is similar to Earth's, as can be seen in pictures taken by Cassini and its probe which transmitted data from the surface of titan for a short time a couple years ago.
This article caught my attention since it talks specifically about liquid on another planet, something not altogether unheard of. Theories of underground oceans on Europa and frozen oceans and rivers on Mars are common and well-supported. But it is worth noting that the search for liquid water is an essential early step in the search for life, but it is not as easy as looking for places where liquid has been. Many elements form a liquid in the range of temperatures between the Earth and the outer solar system, which is why we need methods like spectroscopy and sample analysis to determine the nature of the liquid.