The Yale University Open Access image library.

[Redrobes]

I dont know if this has been posted before but its a great resource. Yale uni has decided to open up loads of its images for open accesss. I will have to check it that means public domain or what, but it looks like a great collection. First of all its 250,000 images and secondly, a lot of them are in a format like a museum curator would want. I.e. many of the items in there are on clean backgrounds so can be converted to top down icons. Anyway, start here...

http://discover.odai.yale.edu/ydc/

but check out something like this:
http://ecatalogue.art.yale.edu/image...962&size=large

Theres loads of maps in there too which I started out on but I found the items particularly useful. Pottery, mosaics, floor tiles, reliefs, etc all good for dungeon & adventure art.

EDIT: Holy moley - theres 29000 coins to look at. Its really mind blowing amount of stuff to wade through.