The MET Museum has just made 375,000 high-res images free for the public to download with no restrictions through Creative Commons Zero. This is great news for artists, designers and anyone interested in viewing fabulous pieces of art throughout the ages. 200,000 public-domain artworks have already been digitally catalogued. The best part is that you are fee to use the images for whatever you want. For me, they make great references for illustration subjects. Click this link to start searching the archives!
I am currently researching ancient gold objects for a new illustration project.... these are a few out of 1,000's of images that sparked my interest. Thanks to the MET for offering this awesome resource.