Abandoned is an iPhone application by design group FORM that allows you to find modern day ruins to explore and photograph. There are many people who enjoy photographing abandoned and run-down locations, and can easily find and share such locations using this app.
In addition to providing a list of locations near you, you can also read and write comments on locations and maintain a personal, private log of locations you’ve found.
The application costs $2.99 and is available from the App Store. I think this would make a really good free web application if someone has the time to build it.