Tunnel in the Sky | written by Heinlein in 1955
Foundation Trilogy.
And pretty much anything by Larry Nivan, like Ringworld.
Science Fiction is often best read as an adolescent and therefore some of the most memorable and significant works in a readers lifelong list are going to be less than undying adult literature. That does not mean they aren’t great but just when comparing them to other genre you have a disconnect.
I’ll add one — The Cities in Flight series.
I don’t read much science fiction, but I found “The Andromeda Strain,” “Brave New World” and “Demon Seed” intriguing.
A Canticle for Liebowitz - Walter Miller
Mansions of Space -John Morrisey
Amber - Roger Zelanony
Our teacher read A Wrinkle in Time to us in the 7th grade, 1961. I’ve been hooked on SF ever since.
Foundation series.
Fahrenheit 451.
Bookmark, ahem
I enjoyed the Skylark and Lensman series by E.E. Doc Smith years ago. Could just be me. 😊🙌
A Canticle For Lebowitz.
The first third is absolutely magnificient and more than compensates for the final third.
Dune
Cities in Flight
Foundation Trilogy
Star Wars! Duh!?
Foundation trio
Stranger in a Strange Land
Mote in Gods Eye
Jules Verne’s writings would be up there.
But then, the next book:
Robots and Empire is part of Asimov's consolidation of his three major series of science fiction stories and novels into a single future history: his Robot series, his Galactic Empire series and his Foundation series. (Asimov also carried out this unification in Foundation's Edge and its sequel.)But again If you have to describe the total works of Asimov's future history, you have to consider Heinlein's major works.
I have taken a stab at writing the best Sci Fi book. Been working on it 32 years. It is unique, for sure. Anyone want to do a free read, I need readers. Just mail me. It’s online.
Out of the Silent Planet trilogy, Brave New World, 1984, John Carter Series, On The Beach, Dune. Those are some of my favorites.
Immortality, Inc. By Robert Sheckley
Harrison Bergeron By Kurt Vonnegut
Can’t think of a third right now.
https://www.gutenberg.org/ebooks/subjects/search/?query=science+fiction
much free early science fiction here which is the best
the periodicals have very good short stories
https://www.gutenberg.org/ebooks/subject/9016