Art History 

Oxford Art Online
- Oxford's combined art databases, searchable uniformly or individually

Encyclopedia of World Art - hardcopy only
- 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

Symbol Dictionaries

Artists Biographical Dictionaries

Period Dictionaries

Grove Dictionary of the nineteenth Century

Decorative Arts

Oxford Encyclopedia of the Decorative Arts