Ohio Trespassers is one of the coolest sites. A couple of intrepid explorers have made it their mission to trespass onto all the unusual and out-of-the-way sites they can find, and collect photo evidence. Abandoned factories, graveyards, barns, castles, hospitals, tunnels, and insane asylums all yield up their secrets.
Immortelle.net offers histories and visual tours -- including virtual 360 panoramic views -- of New Orleans' fascinating cemeteries, which resemble the French-style cities of the dead.
Forgotten NY is an enormous site exploring hundreds of forgotten nooks and crannies of New York City in words and pictures. Not just abandoned and old places, but also unusual ones. Categories include old signs and advertisements, subways and trains, cemeteries, cobblestones, street scenes, trolleys, and more. This site is just massive.
All of this reminded me of Ghost Town, that story of the woman Elena who documented her trip through the desolate lands of the Chernobyl area. It turns out that her story is exaggerated if not entirely fabricated -- apparently she did not daringly forge into forbidden territory alone on a motorcycle as she claims, but went on a guided excursion in a car with her husband -- but however true the frame narrative, the pictures themselves are still (mostly) real (a few of them might be staged), and very evocative. (More info: this thread explains why it's not true. Here is the website for the private tour she went on.)
My earlier post, "Abandoned places," can be found here.