This site has gazillions of highres images of microscopic
photographs of lunar mineral samples. Some of the images
are pretty spectacular and make great wallpapers.
http://ser.sese.asu.edu/cgi-bin/DPSC_Binderview.pl?missionid=ap15¬...
For instance, one of my favorites is:
http://ser.sese.asu.edu/cgi-bin/DPSC_Position.pl?position=ap1505_04_18
I have no idea what sort of license might be associated
with them, but you'd think apollo photographs would be
public domain (maybe :-).
Just tossing it out in case someone wants to sort through them
for candidates.