Check out the website of the Visual Resources Center at Wright State in the Creative Arts Center.
Or use these related research guides:
Oxford Art Online is a database that has the full text for several good-quality art encyclopedias, including the scholarly Grove Dictionary of Art. A great place to get an overview of an artist or method.
The books on the third floor are organized by the Library of Congress system, which groups like subjects. Sometimes you can find the perfect source simply by browsing titles on the shelves in an area relevant to your interest.
N -- Visual arts
NA -- Architecture
NB -- Sculputure
NC -- Drawing. Design. Illustration.
ND -- Painting
NE -- Print media
NK -- Decorative arts
NX -- Arts in general