It's the industrial pictures that I find most depressing; I found reports on 28dayslater on two factories that belonged to the company where I first worked after graduating. It was technically excellent but commercially useless, after I left in despair it got sold on twice then closed and broken up in the late 90s, yet another victim of incompetent British management.
It was on that site that I once found the most astonishing and beautiful photo of a derelict interior I had seen for years; it's really a photography website as much as an Urbex website.