I am obsessed with this website called Recapturist by photographer Bill Rose. It's a very organized catalog of retro neon signs, many of which have been abandoned, all across America. Bill has no definitive list of signs to get through, but his efforts so far have captured the beauty and elegance of these neon lights that are slowly being replaced by other signage and LEDs.
As you can imagine, he's traveled a lot. There's even a handy map of sign locations if you want to trail him in his search.