"The Timeline is a chronological, geographical, and thematic exploration of the history of art from around the world, as illustrated by the Museum's collection" (About the Heilbrunn Timeline of Art History). The Timeline, researched by the Museum's curators, conservators, and educators, continues to be expanded.
The Metropolitan Museum of Art has timelines from 8000 B.C. to the present. Besides the timelines, there are World Maps, Thematic Essays, Works of Art, and Indexes.
Research Tools & Vocabularies at the Getty Institute
The Archives (part of the Smithsonian Institution) provides access to letters, scrapbooks, manuscripts, financial records, photographs, sketches, film, audio, video recordings, and oral histories on American Art which are located in the United States. Under "Research Collections" you have the option of browsing the collections alphabetically, browsing by topic, browsing Oral History Interviews, viewing all fully digitized collections, or searching the Image Gallery. The section under Additional Resources includes the Smithsonian Institution - Archives, Manuscripts & Photographs Catalog (SIRIS).
The Classical Art Research Centre includes 20 databases which can be searched individually or in a combination, a dictionary of Greek and Roman individuals and places, and information on topic such as classical art, pottery, gems, and sculpture.
The University of Wisconsin Madison General Library System maintains the Digital Library for the Decorative Arts and Material Culture. This digital library provides electronic texts and facsimiles, image databases, and web resources relating to decorative arts, in particular Early America.
Alan Liu and others at the University of California, Santa Barbara maintain Voice of the Shuttle. This website has a page dedicated to Art History with categories such as general art history resources, region (Africa, etc.), architecture, art theory & politics, technological analyses of art, museums, galleries, institutes, & centers, auctions, journals, academic departments & programs, and course syllabi & teaching resources.