Jet Propulsion Laboratory's Visions of the Future posters
I love this set of posters from JPL's Vision of the Future series. The latest batch of 3 posters are made by Invisible Creature to help promote intergalactic space travel. Every poster in this series is free to download and use as you see fit. You can print them out as big as you want and plaster your whole room with them. Pretty fantastic, no?