Oxford Art Online includes the following individual titles:
Chilvers (ed) Oxford Dictionary of Art and Artists
Chilvers (ed) The dictionary of modern and contemporary art
Clarke, Michael (2003) The concise Oxford dictionary of art terms.
Darvill, Timothy (2008) The concise Oxford dictionary of archaeology
Morgan, Ann Lee. (2007) The Oxford dictionary of American art and artists
Hall, James Dictionary of subjects and symbols in art. Reference - N7560 .H34 2008
Turner (ed) Dictionary of Art - Reference - N 31 .D5 1996
Thames and Hudson dictionary of art and artists - Reference - N33 .T43 1985
MetPublications From the website: MetPublications is a portal to the Met's comprehensive book and online publishing program with close to 700 titles published from 1964 to the present. MetPublications includes a description and table of contents for most titles, as well as information about the authors, reviews, awards, and links to related Met titles by author and by theme. Current titles that are in-print may be previewed and fully searched online, with a link to purchase the book. Collections.
Getty Institute Publications Virtual Library Free digital backlist titles from the Getty Publications Archives.
Brooklyn Museum publications - selections from books published by this museum are available here - read more about the project on the Brooklyn Museum Blog
Los Angeles County Museum of Art Reading Room from the website:The Reading Room is a special corner of lacma.org dedicated to catalogues and brochures of exhibitions past. These are out-of-print, hard-to-find publications available here in full for free. From a unique set of publications focused on the Southern California art scene to rare books about German Expressionism, modern art, Southeast Asian art, and more, the catalogues and brochures here reflect the depth and breadth of LACMA’s collection and exhibition history.
The MMA has made the records and images of almost 500,000 items in their collections freely available with open access rights.
"...all images of public-domain works in The Met collection are available under Creative Commons Zero (CC0). So whether you're an artist or a designer, an educator or a student, a professional or a hobbyist, you now have more than 375,000 images of artworks from our collection to use, share, and remix—without restriction."
Read more on Open Access at the Met.