I discovered an incredible site today -- http://www.opacity.us/ -- full of amazing photographs of abandoned "urban ruins". Per the web site, "This site is dedicated to documenting various abandoned places through both text and photographs; recording their transformations through time before they are demolished". Tom Kirsch explores these ruins, sometimes with permission, sometimes, um, not, and captures the most amazing photographs.
This is the kind of photography that I love. I love old things, things with mystery and curiousity about them. I'm fascinated by his work.
Take some time and visit his site!