Frederick Sommer's amputated foot photo for certain. The nun who wrote into Aperture certainly helped generate some sales for them... I find the dead coyote pictures and the chicken pictures unsettling as well.
David what's his name - English (or French?) guy who does portraits of (very) young women nude. But there is nothing unsettling about the pictures other than the age of his models from what I have seen of them.
Those creepy shots of children in costumes by Anne Geddes are stomach turning. And the guy who shoots the Weimaraners.. Absolutely frightening...