How to Be Well-Read in a Science Fictional Universe

Our retired lit teacher and genre enthusiast comes up with 144 books that make a highly subjective, personal, and idiosyncratic core reading list in SF. He has excluded Fantasy because he believes that it should be considered a separate literary genre and therefore should have its own list. Feel free to disagree with some or all of the books listed here; the idea was to create a starting point for debate and discussion.