Unlikely SF authors?

I've read lots of traditional sci-fi and fantasy. Recently, I have been looking for some more offbeat reads. Can you think of any "unlikely" sci-fi authors?

What I mean is, can you think of any authors that many people wouldn't usually associate with the sci-fi/fantasy genre, but that indeed contributed some works. I've come up with the following:

Conan Doyle (Professor Challenger series) D.H. Lawrence (The Rocking-Horse Winner) Kurt Vonnegut (Report on the Barnhouse Effect) Mark Twain (Connecticut Yankee)

I realize that these are mostly "classic" authors, but these are the ones that came to mind first.

Any ideas?