The Yale Digital Commons has millions of images of objects from their museums, libraries, and archives availably freely online. Because of a new open-access policy, you can currently view a quarter of a million images, with more access to come.
The best way to search the collection is through the Advanced Search option. This lets you immediately limit your results to images freely available. You can also limit to the different Yale University institutions or by collection.
The overall database is extremely diverse. Collections include ancient art, botany, and paintings and sculpture. There are also iTunes playlists of topical lectures and poetry readings. Because new material is continuously being added, bookmark this site and check back often!