Google Images, a search engine for online images
ORB, The Online Reference Book for Medieval Studies
Art History Resources, Christopher Witcombe
e-Catena, Early Christian Writings
Museums, complied by the University of Michigan
The Archives of American Art, The Smithsonian Institutes research center housing the history of American art
Art and Architecture Collection, New York Public Library
Classical Art Research Center and The Beazley Archive, University of Oxford
The European Library, online portal to 48 national libraries in Europe
Internet Ancient History Sourcebook, compiled and edited by Paul Halsall, Fordham University (part of the Internet History Sourcebook Project)
Dictionary of Art Historians, Department of Art, Art History and Visual Studies, Duke University
Metropolitan Museum of Art Collections Database
Warburg Institute, University of London
Bibliography of the History of Art (BHA) & the Repertoire de la Litterature de l'Art (RILA), covering the history of Western Art through Late Antiquity, 1975 - 2007, Getty Institute