At 5:55 pm EDT today, the Mercury probe MESSENGER will make its closest approach to the planet, shooting over the surface at an altitude of a little under 142 miles. Above is the planet from MESSENGER's point of view on Sept. 28 when it was 337,000 miles from flyby.
From the MESSENGER mission website:
This NAC image of a sunlit crescent Mercury was taken 44 hours before the spacecraft's closest pass to the surface. Visit the interactive visualization tool to examine in detail the instrument observations planned for the flyby. Starting at 3:45 pm EDT today, the visualization tool can be run in real-time, showing the planned observations on the website at the same time that the MESSENGER spacecraft will be performing the actual observations. The images and other measurements collected by MESSENGER during the flyby will begin to be transmitted to Earth just before midnight tonight.
Keep an eye on the MESSENGER website, that will be the place to see the first new images of the Solar System's smallest planet...