Smithsonian Institution's Office of Imaging and Photographic Services (RESTRICTIONS:  You may only use these photos for personal, educational or NONCOMMERCIAL uses - Read Copyright notice at the top of the page.)
http://photo2.si.edu/


ARS (Agricultural Research Service) Image Gallery on animals, crops, education, field research, fruits & vegetables, illustrations, insects, lab research and plants.
http://www.ars.usda.gov/is/graphics/photos/

Art Images for College Teaching (AICT) by A. T. Kohl, EXCELLENT historical photos here, Egypt, Medieval, Western, Renaissance, Baroque.
http://arthist.cla.umn.edu/aict/index.html

Coin Page (Describes and shows images of an enormous collection of coins)
http://www.coinpage.com/

Free Public Domain Images - small collection
http://www.pdimages.com/web6.htm

GRIN - Great Images in NASA - Science photos and more in high resolution!
http://grin.hq.nasa.gov/

JSC Digital Image Collection (NASA) - Includes over 9000 NASA images
http://images.jsc.nasa.gov/

NASA Multimedia Gallery (Images, video, and interactive features)
http://www.nasa.gov/multimedia/highlights/index.html

Natural Resources Conservation Service (NRCS) Photo Gallery (You must use a special credit line to use photos - Read)
http://photogallery.nrcs.usda.gov/

NOAA (National Oceanic and Atmospheric Administration) Photo Library - search 20,000 NOAA images Plus more than 10,000 new images, oceans, hurricanes, hurricane Katrina and more.
http://www.photolib.noaa.gov/

Planetary Photojournal from NASA - Pictures of ALL THE PLANETS IN SPACE!
http://photojournal.jpl.nasa.gov/

Public Health Image Library (PHIL) from Centers for Disease Control and Prevention - Includes pictures of Influenza, Natural Diseases, Bioterrorism and electron Micrographic Imagery.
http://phil.cdc.gov/Phil/default.asp

US Fish and Wildlife Service: Pictures/Graphics (Images are in the Public Domain UNLESS it is noted that it is copyrighted - Read)
http://pictures.fws.gov/
 

Clip Art

Animation Factory (3D animations and clipart)
http://www.animfactory.com/

Awesome Clipart for Kids, Teacher & Family
http://www.awesomeclipartforkids.com/

Clip Art Connection
http://www.clipartconnection.com/

Clip Art Gallery from DiscoverySchool
http://school.discovery.com/clipart/

Graphic Maps
http://www.graphicmaps.com/clipart.htm

Page Resource (backgrounds, dividers, images, and links)
http://www.pageresource.com/graphics/index.html

Abraham Lincoln
http://showcase.netins.net/web/creative/lincoln/resource/freepix.htm

Images from the History of Medicine (IHM) from National Library of Medicine
http://wwwihm.nlm.nih.gov/

Images of American Political History
http://teachpol.tcnj.edu/amer_pol_hist/

Map Collections: 1500-2003 from American Memory, Library of Congress
http://memory.loc.gov/ammem/gmdhtml/gmdhome.html

Moving Image Archive from Internet Archive
http://www.archive.org/movies/movies.php

American Memory from the Library of Congress
http://rs6.loc.gov/amhome.html

Metropolitan Museum of Art, New York
http://www.metmuseum.org/home.asp

NetVet (Links-site to collections with varying restrictions of use.  Animal, zoo, wildlife, Africa and more.)
http://netvet.wustl.edu/pix.htm

New York Public Library Picture Collection Online
http://digital.nypl.org/mmpco/
Collection of 30,000 digitized images from books, magazines and newspapers as well as original photographs, prints and postcards, mostly created before 1923. (although these images are in the public domain, the library charges a usage fee.  I have included this site because it does have some hard to find and useful photographs.)

http://digitalgallery.nypl.org/nypldigital/index.cfm (although these images are in the public domain, the library charges a usage fee.  I have included this site because it does have some hard to find and useful photographs.)