I'm just now starting the process of assembling a collection of art assets to use in my campaign. Some things, like the map for the campaign setting, I'm freehanding in Inkscape. Other stuff I've pulled from the old and forgotten 3.5 archives on the D&D site, such as maps and NPC portraits.* Now I'm wondering: what other sites have you found useful for this kind of material?
*There are actually TWO archives, that don't link to each other. One has the maps, the other has the portraits. It's not too hard to find either, once you know they exist.