We have imaged the other side of Mercury
Boston University astronomers did it in 1999:
http://sirius.bu.edu/planetary/mercury/baumgardner2.html
http://sirius.bu.edu/planetary/mercury/baumgardner.pdf
But so did an amateur astronomer:
http://www.space.com/scienceastronomy/solarsystem/mercury_view_000531.html
http://cdsaas.u-strasbg.fr:2001/AJ/journal/issues/v119n5/990240/brief/990240.abstract.html
Mercury has at least one big crater on the side not seen by Mariner 10. And let us not forget the ice at the poles.
