The Messenger mission in conjunction with the USGS has released an updated composite map of the surface of Mercury. The new surface map combines images from the three Messenger flybys and the Mariner 10 mission from the 1970's and covers 97.72% of the surface.
This new surface image was developed for the purpose of helping mission planners identify key observation targets during the orbiting phase of the mission. It has a surface resolution of around 500 pixels and comprises of images taken across a range of illumination conditions, spatial resolutions and the decades. To create the composite image required the careful creation by hand of thousands of control points to ensure that all the various projection effects are correctly compensated.
The full mosaic is available for download via the Map-a-planet website.