I found a company on Amazon that sells High Quality Space photos called New Horizon Aviation.
They offer posters from 11×17 all the way up to 24×36.
The posters are quite affordable and a must for anyone into Rocketry, Astronomy or even a Pilot Man Cave.
Here is a selection of some I found interesting:
Apollo 8 Earthrise
Star Cluster NGC 2074
NASA Andromeda Galaxy
Hubble Ultra Deep Field
LLC Pillars of Creation
Saturn
Gould Aero 