Oxford Art Online - Oxford's combined art databases, Dictionary of Art and Encyclopedia of Esthetics, searchable uniformly or individually. Scholarly entries signed by authorities in the Medieval area, as well as all others.
Oxford Dictionary of the Middle Ages - online scholarly encyclopedia. Also in print in Perkins/Bostock and Lilly Reference D114 .O94 2010.
Encyclopedia of the Middle Ages - another more concise encyclopedia of medieval topics
Arts and Humanities Throughout the Eras - see the volume on Medieval Europe.
Pilgrimage: from the Ganges to Graceland: an Encyclopedia Perkins/Bostock Reference BL619.P5 D38 2002 (also online in History Reference Online)
Religions of the World, Second Edition: A Comprehensive Encyclopedia of Beliefs and Practices
Divinity Library Reference BL80.3 .R45 2010 (also online in History Reference Online)
Enciclopedia dell’arte medievale. 12 vols. Rome : Istituto della Enciclopedia italiana, 1991-2002. Divinity and Lilly Reference N5965 .E52 1991 - excellent plates and bibliography, even if you don't read Italian.
Encyclopedia of World Art - hardcopy only. Lilly Reference N31 .E4833 1959
- older, but longer essays on art topics and issue + half of every volume is plates, may in color; - older
Pelican History of Art (series) Lilly Reference [various titles depending on period] Lilly N5300.P38
- the standard English-language history of art. Continuously updated. + extra images; good beginning bibliography
- Renaissance volumes include
Dodwell, C. R. Pictorial arts of the West 800-1200. New Haven [Conn.] : Yale University Press, 1993. Lilly Reference N5300 .P456 v.2
Frankl, Paul. Gothic architecture; revised by Paul Crossley. Rev. ed. New Haven : Yale University Press, 2000. Lilly N5453 .F683 2000
Hall, James. Dictionary of subjects and symbols in art. Edition 2nd ed. Boulder : Westview Press, c2008. Lilly Ready Reference N7560 .H34 2008
Artists Biographical Dictionaries
Dictionary of artists - "Benezit". Paris : Gründ, 2006. 14 vols. Lilly Reference N40 .D5213 2006
The rise of the medieval world, 500-1300 : a biographical dictionary / edited by Jana K. Schulman. Westport, Conn. ; London : Greenwood Press, 2002. Perkins/Bostock Reference CT114 .R57 2002
Dictionary of the Middle Ages / Joseph R. Strayer, editor in chief. New York : Scribner, 1982-1989. Lilly Reference D114 .D5 1982 - general reference dictionary of the medieval period. Good for general historical overview and discussions of people and themes.
Crosby, Everett Uberto. Medieval studies : a bibliographical guide. New York : Garland Pub., 1983. Lilly Reference CB351 .C767 1983 - annotated bibliographies organize articles by topics much more narrowly than catalogs and, they're just the better works.
Grove Encyclopedia of the Decorative Arts - a decorative arts dictionary strong on medieval terms and objects
The Art of Gothic : architecture, sculpture, painting / edited by Rolf Toman; photography by Achim Bednorz.
Cologne : Könemann, c1999. Lilly NA440 .A78x 1999 - most surveys are poorly written fluff. The Könemann series on architecture combines great (really great) plates, reliable text (quoting famous art historians) in a readible tome.
Grodecki, Louis. Gothic architecture / in collaboration with Anne Prache and Roland Recht. New York : H. N. Abrams, 1977, c1976. Lilly NA480 .G7613 1985 - part of the History of world architecture series, includes cut-aways of buildings and spectacular plates.
SEE ALSO A LIST OF STARTER BOOKS UNDER THE "Starting Your Paper" TAB