Well, here goes!
Evidence of an ancient stream. From NASA
The Curiosity rover recently discovered what appears to be the bank of a dried up stream on the surface of Mars. The circled rock appears to have been worn smooth by water erosion, as do the small pebbles on the stream bed. The overhanging rock looks similar to the erosion of small bodies of water here on Earth.
This isn't the first evidence that Mars was once running with water, but it certainly lends more credence to the notion. Too bad Mars isn't still as wet as it once was.