Where is a good source for serious math (wall-size) posters? Where is a good source for math wall posters that give glimpses of serious and beautiful mathematics?
I'm a faculty member looking to find some wall posters (e.g. 2 ft x 3 ft) to hang in a handful of display cases around our department. I'd like the posters to be eye-catching and cool (maybe even inspiring!), and also deal with serious mathematics - not be trivial, vague, or snide.
Any ideas?

One source for posters that may fit your description (though I don't know about the size) could be  http://www.ams.org/samplings/mathmoments/mathmoments 
