Fort Mott
Fort Mott is along the Delaware River, in Fort Mott State Park just south of Wilmington. It was quite a drive; the gas set me back more than I care to admit. The fort itself was built to protect Phildelphia. It's pretty cool looking, and I wouldn't mind going again.
It's not an abandoned town per se, but Fort Mott is a great exercise in civic forensics. The entire place is very well preserved and, aside from the ranger station/gift shop, which isn't an original structure anyhow, the fort's major archaeological features have been preserved. The entire place was decommissioned when the guns were removed during WWII, essentially giving us an eyewitness to this particular place-death. I've considered giving forensic tours of this site, but I'm too busy to do it right now. If anyone is willing to plop down $1000/person, though, I might just make the drive. I need books.