Download 11,710 Free-to-Use Photos of Roadside Americana:
The 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.
These are great and free to use! You can view all of them at the Library of Congress, though many are easier to review on Flickr.