The MARSIS radar experiment aboard the ESA's Mars Express satellite will come a bit closer in late June when the second dipole boom is deployed. These 20-meter-long structures will send very low frequency waves which will penetrate up to several kilometers deep. Reflections will indicate any sub-surface interface, including possible water or ice deposits (a nice diagram is here. ) Subsurface water is the best chance for life on Mars, as surface uv irradiation is very intense.
The antennae had been loaded in a telescoped configuration and there has been a fair amount of hassle getting the first one fully extended. What I especially appreciate about this saga is how it underscores that machines in space do not always behave as predicted in ground testing, so there's quite a lot of seat-of-the-pants adjustment going on.
Subsurface water may also be all there has been on Mars for some time. Some other work suggests that the atmospheric methane detected on Mars might be coming from breakdown of olivine by water. This "mineral source" (rather than microbial source) theory of ongoing methane production would require that the olivine had been kept dry since its creation in lava flows-- in this case, some 3 billion years. But in that case, where's the water coming from now?
UPDATE: More on the recent olivine-methane work is in last week's Nature .
UPDATE, 16 June: The second boom deployment seems to have gone smoothly but the gyroscope data are not yet in. Looking for water could start as soon as next week.