Part of the problem that any Post Apocalyptic DM faces are grand show piece locations for his intrepid explorers from the retro future to explore. There always needs to new ones and brand new experiences for them. Io9 recently solved part of this dilema for me with a fantastic overview of the 1964- 65 World's Fair in pictures and a great article. The echoes of this event and the marching of a Future That Never existed are right over
Pavilion after pavilion of locations to loot,explore, and exploit are right around the corner here and are perfect fodder for your old school post apocalyptic games. Seriously these locations practically write themselves into your favorite adventures!
These are only a few of the images that are there. They've got a ton of photos that really bring that Retro future vibe from the past right home into your old school campaigns!
For added weirdness imagine your players walking around on Carcosa or some other retro science fantasy campaign and coming face to face with these locations with weird artifacts and tribes.