I just stumbled upon a resource that might be useful to you as a GM or as a deity.
The Getty Project recently open-sourced most of their images.
http://www.getty.edu/art/
There is all kinds of art in there, including fantastical, mundane, and plenty of images from mythology.
I may use this for some art on the Pantheon in the future. As a GM or game designer, it could be a good resource if you're going to publish something and are worried about copyright.
What other good art resources are out there?