Neatorama reader Rich B. sent in this one: the very first McDonald's store in Des Plaines, IL. Check out Speedee touting the 15¢ price and the fact that they had sold over 1 million - read that: ONE MILLION! - burgers!
http://www.flickr.com/photos/eurovancation/1153501544/ [Flickr] - Thanks Rich!
Previously on Neatorama: Old McDonald's Sign
[Update 8/28/07: Oops, Technically not the first McDonald's. The Des Plains McDonald's was the ninth store (but the first one opened by Ray Kroc). Although it is now referred to as The Original McDonald's, the very first one was opened by Dick and Mac McDonald in San Bernadino, California. Wikipedia has more info: Link | See also: World's Oldest Surviving McDonald's in Downey, CA (the fourth one built) - Thanks Matt, John, and K!
http://www.downeyca.org/visitor_mcdonalds.php