Remembering Nagasaki -- In observance of the 50th anniversary of the bombing of Hiroshima and Nagasaki, San Francisco's Exploratorium has created this "photographic journey," featuring the stunning photographs of Yosuke Yamahata.
Information Age: People, Information & Technology -- This site, curated by the Smithsonian's National Museum of American History, explores the ways in which electronic technology has altered American society over the last 150 years.
1492: An Ongoing Voyage -- This site is an excellent example of how to blend a ton of textual information with a few key photos to produce an extremely informative exhibition. Brought to you by the Library of Congress.
The Great Adventure -- This portion of the Canadian Museum of Civilization is a truly interactive experience, allowing visiters to (virtually) visit different parts of the world.
Art Crimes: The Writing on the Wall -- Here's a gallery of graffiti art from around the world, from Prague to Paris, from L.A. to D.C.