NewScientist is reporting that the rover Opportunity has taken pictures that appear to be small ponds of liquid water on the surface of Mars.

The claim is from pictures taken two years before in the crater Endurance, recently analyzed.  Many scientists dispute the findings because they believe that liquid water cannot exist on the surface of Mars due to the thin atmosphere.  Other's are challenging those assumptions and the photographs are tantalizingly 'evidence' that seem to show blue areas that are perfectly flat, and show reflective properties.  Some even claim to see pebbles within the 'pool'. 

Here is the article

and here is the picture:

Additional evidence was discovered last month from the serendipitous analysis of the tracks left behind the rover Spirit from it's dragging wheel that malfunctioned which leaves a trench in it's wake.  That trench shows strong evidence of silica which is the result of water interacting with the soil.  Link here.