The Victoria and Albert Museum has a great many excellent online resources, and their collections are very easy to search. I highly suggest their site if you have a project that requires you to look for art by type. For example, they have links to architecture resources, books, furniture, glass, print, and many, many other types of art and design. My favorite part, however, is their wig generator. It lets you play with the towering hairstyles of historical nobility, and you can put a boat on someone’s head.
Website: The Victoria and Albert Museum
Humanities Scholars 