Maybe I didn’t emphasize this when I started the thread, but the dozen books I listed were not MEANT to be a complete list. Good lord, how could they be!
There’s some great suggestions here, but let me repeat that I’m looking not just for good sci-fi writing, but work that is canonical to the field. So let’s pretend we’re planning to teach a course in sci-fi literature for someone who’s never read any. So we have to be discriminating, and not make a list with a thousand books on it. The student should come away having an understanding of the history and development of the genre, an idea of its thematic scope (i.e. sociological themes, psychological themes, humorous writing, etc.), the common tropes (space travel, time travel, the socially dangerous technological development, apocalyptic events, utopic societies, the evil mad scientist, the scientist as victim of his own experiments, etc.) and a taste of the most famous authors. To put it another way, if you couldn’t stand up in front of a class and explain for an hour what’s important about the book, it should be left out. So being a good yarn isn’t enough, it has to have offspring - stylistically, thematically, philosophically, etc.
Short stories were mentioned, and it’s true that a lot of the best sf is short stories, at least to my experience. But just to keep things structured, let’s do short stories next semester; we’ll do novels this time. Similarly, movies and shows like Star Wars and even more, Star Trek, have been enormously influential on the scifi of the last thirty years; nevertheless, I suggest we keep to novels so we can keep some kind of focus in our picks. Finally, bookstores lump sci-fi in with fantasy works because the readership tends to be similar; nevertheless, works that are not clearly one or the other are pretty rare to my experience (though they do exist). I’m looking for actual Sci-Fi right now. We’ll do fantasy next semester, too - in fact that might make an interesting spin-off thread.
As for the notion that there can be no canon for sf, balderdash! There’s a canon for English literature itself - is sf broader than that? Shakespeare is in the canon, Jackie Collins is not; I think we can be similarly discerning with sf authors and their works. To claim otherwise is the sort of nonsense (although seen from the other side) that results in the standard English canon containing so few science fiction works because sf is considered “merely” genre writing. When sf fans suggest that the work is somehow privileged from the same standards of criticism that apply to every other area of writing, they just exacerbate the problem.
Getting to specifics:
I know from reading them, or by reputation, that the following suggestions are good additions to the canon list.
Ursula LeGuin-
The Left Hand of Darkness
[A Wizard of Earthsea is excellent, but not SF. Similarly with Zelazny’s Amber series, great as they were, and obviously again for Lord of The Rings. I haven’t read Dragonriders of Pern, but that, too, sounds more like fantasy to me than sf, no?]
Philip Jose Farmer-
Riverworld
[I haven’t read this one either, but it is often referred to as a seminal work in sf.]
William Gibson-
Neuromancer
Arthur C. Clarke-
2001: A Space Odyssey
[Other works of his were mentioned, but not this one! It is obviously the defining novel of his career, even if some other books had powerful things to recommend them and may have been better in some ways]
Robert Heinlein-
Time Enough For Love (Lazarus Long)
The Moon Is A Harsh Mistress
Stranger in A Strange Land
[I found this book irritating and dated. Heinlein has many better books to his credit; however this is, IMO, the most broadly influential of his novels by far.]
Ray Bradbury-
The Martian Chronicles
Farenheit 451
Edgar Rice Burroughs-
Princess of Mars
[Okay, it’s hokey. But it epitomizes a type of pulp sci-fi that was once definitive of the genre.]
Daniel Keyes-
Flowers For Algernon
Larry Niven-
Ringworld
I can hardly believe I almost overlooked one of the absolute best, deepest, most influential science fiction works of all time:
Mary Shelley-
Frankenstein
I would also add
Stanislaw Lem-
The Cyberiad
There are many authors who have been extremely prominent at the forefront of the sf genre, but either their best works are short stories (easier to get published, I think), anthologies, or no particular novel stands out as their masterpiece. We can vote on which novel to include for these guys; some suggestions have already been made. Harlan Ellison
Frederick Pohl
Gene Wolfe
L.Sprague DeCamp
Samuel Delaney
John Varley
H.Beam Piper
Or maybe we should just save these guys for short stories next semester. I have 25 novels on my list already!