Personally, I think crazy people or evil people or something so "out there" would be a great narrator. If told well, it's really fascinating to get inside that person's head. And there's probably something amazingly universal about the character that, even if you don't agree with what he thinks or does, you can still understand and, thus, identify with him in some way. Also, I don't think first person means the readers must share the narrator's values. To me, it's as if I'm sitting there and listening someone fascinating (or crazy) telling me a story, with the comfort to know that I can close the book when I feel uncomfortable, then pick it up again at my own pace, safely.