OAIster: union catalog of digital resources
MADID (Yale University Manuscripts & Archives Digital Images Database)
Bridgeman Art Library: art, culture & history images
Masters of Architecture Over 7,000 digital images of slides originally belonging to architects
Parker Library on the Web : Images of 6th-18th century manuscripts from Parker Library in Corpus Christi College, Camden.
National Galley of Art | NGA Images a repository of digital images of the collections of the National Gallery of Art