Google Scholar allows you to search the web for a variety of written work from a variety of academic sources. You can set up the Scholar Preferences to show in your results when an item is available through USD; follow the Scholar Preferences link to the Library Links section on the page. When you access Google Scholar through the link below, that preference is already set.
Flickr Commons: Many institutions are contributing images to Flickr Commons including The British Library, California Historical Society Digital Collection, Het Nieuwe Instituut Architecture Collection, Smithsonian Institution, and more.
Library of Congress Digital Collections: Browse through collections such as the Historic American Buildings Survey, Architecture, Design and Engineering Drawings, among others.
New York Public Library Digital Collections: Over 670,000 items digitized from NYPL's collections. New materials are added daily including drawings, prints, photographs, illuminated manuscripts, and more.
The Courtauld Institute of Art: More than 40,000 images are available and it includes collections from the Conway Library. The Conway includes primarily architecture and sculpture.
Visual Collections: The Visual Collections has over dozens of digital image collections from universities, private collections, and museums. The collection on architecture can be found here.
The Great Buildings Collection: More than 1000 great buildings from around the world and across history are listed below and illustrated on this web site and the Great Buildings Collection on CD-ROM, with photographic images, architectural drawings, discussion, bibliography, architect info, and live 3D walkthrough computer models.