ArtServe:art and architecture from the Mediterranean, India, Japan, and Cambodia)

PBase World Gallery (amateur photos organized by country)

American Memory Collection: Library of Congress. (click on "Photos and Prints" and check the "Copyright and Restrictions" section for each collection)

American Memory Maps Collection

America From the Great Depression to World War II: FSA/OWI 1935-1945 American Memory collection

Open ClipArt Library

Daguerreotype Portraits and Views 1839-1864

Department of Agriculture Image Gallery

Graphic Maps.com

Internet Moving Images Archive (read Conditions of Use)

Metropolitan Museum of Art (Please read copyright info on http://www.metmuseum.org/copyright.htm)

NARA's (National Archives and Records Administration) NAIL Search

NASA Commons site on Flickr

NASA Image Exchange http://nix.nasa.gov/

NASA's Planetary Photojournal http://photojournal.jpl.nasa.gov/

National Health Museum (AccessExcellence) http://www.accessexcellence.org/RC/VL/GG/

Picture Collection Online (New York Public Library) http://digital.nypl.org/mmpco/

NOAA Photo Library (National Oceanic and Atmospheric Administration) http://www.photolib.noaa.gov/

Public Health Image Gallery 

Picturing the Century: 100 Years of Photography

Training Reference: Images for Learning Materials http://www.trainingreference.co.uk/free_pictures/index.html

US Air Force Link: Photos and Art. http://www.af.mil/photos/

US Fish and Wildlife Services Images 

Pics4Learning