The U.S. Library of Congress has published over 11,000 high-resolution shots of U.S. roadside attractions, and released the images (to which it had purchased the rights) into the public domain. The photos were taken by architectural critic and photographer John Margolies, who spent forty years documenting his travels along U.S. highways, photographing billboards, drive-ins, diners, car washes, mini-golf, novelty buildings and other roadside constructions.
According to the Washington Post, Margolies wouldn’t photograph a building or object “unless and until he can capture the subject in full sun with a cloudless sky, with no people in the frame.” The result is clear, uncluttered imagery of quirky art and architecture.
The full collection is available at the Library of Congress website, but the Library is also building a Flickr gallery that more elegantly shows off the photos. (That gallery currently has 1,605 images.) As the images are public domain, you can use them any way you please, even commercially.