Artcyclopedia
Currently a free service, the Artcyclopedia allows you to search and browse for artists, the titles of their work and the museums where they are exhibited. As of September 2004, the site boasts indexing, "1800 art sites, and [offering]over 60,000 links to an estimated 150,000 artworks by 8,100 renowned artists."
The link address is: http://www.artcyclopedia.com/