Artinfo.com: art prices and appraisals.
Artvalue.com : Free website of auction results. Includes tips for valuing a work of art.
Blouin Art Sales Index. Free website of auction sales results.
Dealer Stock Books. Getty Research Institute database of Knoedler Gallery records, freely accessible and searchable.
Heritage Auctions: keeps an archive of previous auction results with high-res scans, including film material and posters.
Invaluable: Auction site for art collections. Subscription may be needed to obtain some information.
eMoviePoster.com: Commercial auction site with extensive archive of past results in high resolution (although watermarked).
Knoedler & Co. Exhibition Catalogs Collaborative Project. Catalog of art catalogs from the New York Art Resources Consortium. Includes links to digital versions.
Royal Athena Galleries. Auction site with images of past sales objects. "The world's most extensive selection of fine art of the ancient world."