New Scientist is carrying news that the Mars Express orbiter may have found liquid water using a newly deployed instrument:

Intriguingly, the signal reflected from the bottom of the crater is so strong and appears so flat that it may be liquid water. "If you put water there, that's what the signal might look like," Johnson told New Scientist. But he cautions the data is based on only one pass over the region and could be caused by another material.

As noted, the findings are extremely preliminary. Apparently the radar imaging technique has only been tried once before, on Apollo 17, and the results then were inconclusive. We'll see...