I just stumbled upon this list of the top ten ghost towns, and all of them would make fascinating settings for post-apocalyptic movies.
I think I'd most like to see a film made in the walled city of Kowloon:
"The Kowloon Walled City was located just outside Hong Kong, China during British rule. A former watchpost to protect the area against pirates, it was occupied by Japan during World War II and subsequently taken over by squatters after Japan’s surrender. Neither Britain nor China wanted responsibility for it, so it became its own lawless city."
I've never been to a ghost town myself, I'd be interested in hearing from anyone who has.