Miscellaneous Sites:

Ancient City of Athens  (Photographic archive of the archaeological and architectural remains of Athens.)
Artcyclopedia  (Links to artists' biographies, museum pictures, and periodical articles.)
ArtLex:Dictionary of Visual Art  (Art termology.)
Baroque Architecture of St. Peterburg, Russia  (Historical overview of the architecture of St. Peterburg, Russia.)
Digital Archive of Architecture  (Architecture from the Prehistoric Age to the 20th century.)
Digital Imaging Project: Index to Artists and Architects
Filippo Brunelleschi  (Detailed look into the Renaissance and Baroque designs of Filippo Brunelleschi.)
The First Impressionist Exhibit  
Florence in 15th Century  (Comprehensive look at Baroque and Renaissance Architecture in Italy during the 15th Century.)
George Eastman House  (History of photography timeline.)
MC Escher
Renaissance of the Web  (Cultural links to the Renaissance)
Renaissance: What inspired this age of balance and order? 
The Sculpture Zone  (Sculpture galleries who create and exhibit sculpture from classical to today's styles.)
Time Life Archive  (Past and present photographs with accompanying essays and reports.)
The Vincent Van Gogh Information Gallery  (A comprehensive web site with over 1700 images and 1730 links.)
WebMuseum  (A comprehensive art dictionary including a virtual gallery.)

Museums:
California Museum of Photography
Franklin Institute Museum Hotlist
Isabella Stewart Gardner Museum (Boston)
The Louvre
Los Angeles County Museum of Art
Metropolitan Museum of Art (NYC)
Museum of Fine Arts (Boston)
Museum of Modern Art (NYC)
National Gallery of Art (Washington, D.C.
National Museum of Women in the Arts (Washington, D.C.)
National Museum of the American Indian
Portland Museum of Art (Maine)
Smithsonian American Art Museum
Smithsonian Institute