I don't know what is is about Ohio. Either there's a lot of abandoned, falling-down stuff there, or a lot of people eager to crawl around in it with cameras, but Ohio seems to have more than its share of sites devoted to urban exploration. There's Dead Ohio (covering the northeast), Illicit Ohio (central), Ohio Trespassers (statewide, apparently), and The Ohio Exploration Society (bringing everyone together) -- and if that's not enough, you can find more on the Ohio Exploration Webring, which boasts twenty-one members. The pictures below are taken from Dead Ohio, Illicit Ohio, Ohio Trespassers, and The Ohio Exploration society, respectively.
Abanded: Exploring the Forgotten started as an Ohio-based project, and has since expanded its horizons. It features data sheets, guides, and comments along with photographs of a wide variety of locations, all filed into categories such as hospitals, businesses, locks and dams, or cities.
Mustard Gas Party is a collection of photographic essays documenting numerous old, abandoned, or deteriorating sites. The photography is skillful and wonderfully composed, and the locations fascinating.
Dark Passage is "A New York-based organization providing blind archaeologists with the finest quality flashlights." It's a well-designed site with interesting, poetic narratives accompaning good photographs of copious explorations.
I was going to post all of my links, but I have so many I'd better save the rest for later. Besides, you all get upset at me if I give you too much at once.