NASA occasionally releases new poster sets that you can download and print for free.

There are several different Mars posters in this set.

Mars Explorers Wanted Posters

This is a single poster.

Orion Boldly Going Beyond

Visions of the Future is a set of travel posters to places like Ceres, Titan, Enceladus, Mars, Jupiter and beyond. There are several posters in the set.

http://www.jpl.nasa.gov/visions-of-the-future/