Renaissance Art

The Artchive
http://www.artchive.com/

Artcyclopedia
http://artcyclopedia.com/

Italian Painting of the 15th Century
http://www.nga.gov/collection/gallery/ita15.htm

The Italian Renaissance Art Project
http://www.italian-art.org/main.html

La Renaissance
http://www.ibiblio.org/wm/paint/glo/renaissance/