I've been trying to get a bit better acquainted with the classics of the science fiction genre for the last two years or so. During that time I have read books by Arthur C. Clarke, Robert Heinlein, Poul Anderson, Frederik Pohl, C.L. Moore, Jack Vance, Frank Herbert and Philip K. Dick to name a few. I haven't exhausted the bibliography by these authors by a long shot (and in a few cases I probably never will) but once in a while I like expand my horizon a bit. There are plenty of authors who are missing in this very modest list but one of the more obvious names that comes to mind is Isaac Asimov.
I've looked around a bit and found out the man has a bibliography the size of your average phone book (did they publish his grocery lists too?) so I have no idea where to begin. I could take the easy route and pick up Foundation but picking a book because it is the author's best known work doesn't strike me as a particularly good way of selecting my reading material. So my question to you, if I only ever read one book by Isaac Asimov, which one should it be?