Oxford Art Online (formerly Grove Art Online)
An art encyclopedia, including both articles (with scholarly bibliographies and signed, by scholars) and images. Has good coverage of major classical works, artists, and sites.
Princeton Encyclopedia of Classical Sites. Main Reference and 3rd floor DE59 .P7. Available online at Perseus.
The place to start for bibliography on any classical archaeological site, up to the date of publication (1974).
Lexicon Iconographicum Mythologiae Classicae. Main Reference NX650 .M9 L40.
Look up a mythical individual and find all ancient references, a modern bibliography, and a catalog of illustrations (reproduced in the plates volume) of the myth in ancient art.
In addition to the general indexes and article databases for Classics, see:
Dyabola (1956-present) includes citations for books, chapters, journal articles, festschriften and references to book reviews. It is part of Projekt DYABOLA, a collection of visual and bibliographic databases covering classical, Egyptian and Near East archaeology, Byzantine art history, epigraphy, numismatics, classical history and ancient social and legal history. No full text. An excellent complement for art and archaeology to L'Annee Philologique. It has a specialized search interface; these tutorials by Michael Hughes at NYU are helpful.
ZENON - DAI (Deutsches Archäologisches Institut [DAI]) - Open-access version of Dyabola. In addition to containing records for materials held in the nine libraries of the German Archaeological Institute, ZENON DAI indexes journals, Festschriften and conference proceedings. It covers Greek and Roman material culture as well as Greek and Roman history, epigraphy, and numismatics. For a detailed list of Libraries and their available holdings in Zenon, see the Zenon DAI description.
Combining Art Index/Art Index Retrospective and Art & Architecture Complete, covering over 630 full-text journals, plus full-text books and over 63,000 images. Indexes articles in scholarly journals and museum publications, with good coverage in Classics.