AntiqueClipart.com: Free archives of Victorian, Edwardian, and American Civil War era images.
Bayonet.net: Clipart images and photos related to the U.S. Army.
Clippix Clip Art: Free and public domain clip art images, artist and webmaster resources.
FreePhotos.se: Personal collection placed in the public domain by the photographer.
Images in the Public Domain: A collection of images from Webster's New International Dictionary of the English Language, 1911, G & C Merriam Co. Springfield, MA. Includes machines, insects, mammals, mollusks, reptiles, and agriculture.
Line Art Drawings: Line drawings of wildlife from the US Fish and Wildlife Service. Art can be used with no approval.
Open Clip Art Library: An archive of copyright free images that can be used for any purpose.
Pictures/Graphics - US Fish and Wildlife Service: Photographs and drawings of fish, other animals, and outdoor scenes.
WP Clipart: Line art and other drawings scaled down for use in documents for typical home or small office printing.