Graphics, Images, Art, Photos, the stuff you see with your eyes are part of just about everything digital, and yet when you want to find good copyright-free sources, it can be difficult. There are usually just too many bad (as in pathetic) sites or bad (as in see the thumbnail, buy the graphic) sites in the way. So, I've compiled a short list of sites that you can use to get good, high-quality, copyright-free images for use in whatever work you want.

The best
Open Clip Art

The better

1. http://publicdomainclip-art.blogspot.com/ Public Domain Clip Art a guide to better quality more plentiful public domain royalty free copyright free high resolution images, stock photos, jpgs and clipart free for commercial use.
2. http://www.burningwell.org/gallery2/main.php
3. http://karenswhimsy.com/ Lots of content
4. http://antiqueclipart.com/ Antique Clip Art (small)
5. http://www.art-e-zine.co.uk/

The rest (I actually haven't had a chance to review all these. Some may end up in the 'better' category)

1. http://arthist.cla.umn.edu/aict/ Art Images for College Teaching Free images for students and educators.
2. http://digital.nypl.org/mmpco/ New York Public Library Picture Collection. Many images available for private use.
3. http://freestockphotos.com/ Free Stock Photos
4. http://grin.hq.nasa.gov/ NASA
5. http://memory.loc.gov/ammem/gmdhtml/gmdhome.html Map Collections 1500 to 2004
6. http://nssdc.gsfc.nasa.gov/photo_gallery/ NASA Photo Gallery
7. http://photo2.si.edu/ The Smithsonian Office of Imaging, Printing and Photo Services. Many copyright free images.
8. http://pictures.fws.gov/ US Fish and Wildlife Service
9. http://rs6.loc.gov/amhome.html American Memory Collections. From the Library of Congress. Some images are copyright free.
10. http://sheetmusicweb.com/ Free Sheet Music
11. http://showcase.netins.net/web/creative/lincoln/resource/freepix.htm Images of Abraham Lincoln
12. http://teachpol.tcnj.edu/amer_pol_hist/ Images of American Political History
13. http://www.1art.com/download1.htm Images of oil paintings.
14. http://www.archives.ca/ National Archives Canada
15. http://www.ars.usda.gov/is/graphics/photos/ Agricultural Research Image Gallery Hi res images, free to use.
16. http://www.awesomeclipartforkids.com/ Awesome Clipart for Kids
17. http://www.barrysclipart.com/ Barry's Clip Art
18. http://www.coinpage.com/ Public Domain images of coins
19. http://www.free-photographs.net/ Free Stock Photography
20. http://www.freefoto.com/index.jsp Free Foto
21. http://www.freeimages.co.uk/ Free Stock Photos
22. http://images.google.com Google Image Search
23. http://www.history.navy.mil/branches/org11-2.htm Naval Historical Center
24. http://www.imageafter.com/ Free Photos
25. http://www.metmuseum.org/ The Metropolitan Museum of Art. Some pictures are available for personal use.
26. http://www.morguefile.com/ The Morgue File. Almost 12,000 high res photos free for private and public use. Don't let the name mislead you. This is nothing to do with morgues.:-)
27. http://www.ocean98.org/galry01.htm Ocean98
28. http://www.pdimages.com/web6.htm Small collection
29. http://www.postmodern.com/~fi/sharkpics/clipart/clip.htm Free Pictures of Sharks
30. http://www.seds.org/messier/ The Messier Catalogue.
31. http://wwwihm.nlm.nih.gov/ Images from the History of Medicine

More Info

The US Copyright Office gives the legal details.
The Cornell University Copyright Information Center has a good table explaining when works fall into public domain
however, they omit (in the chart) that an author could have designated a work as 'public domain'. Also, I'm sure they bring it up elsewhere that much of the impetus behind efforts such as the LGPL and Creative Commons licenses is to simplify authors ability to make works that are sharable under the law rather than the draconian automatic policies of current US legislation.

The Franklin Pierce Law Center has a good collection of information about copyright among other legal issues.
Thanks to http://www.altered-book.com/copyright-free-images.html and other sites for helping me generate this list