All of the Heinlein "juveniles": Rocket Ship Galileo, Starman Jones, Space Cadet, Podkayne of Mars, and so forth. Stranger in a Strange Land also cannot be omitted from this list, though it is certainly *not* a juvenile. Starship Troopers and The Moon is a Harsh Mistress as well.
Asimov's Robots stories.
Arthur C. Clarke's 2001 and Rendezvous with Rama.
If you don't mind multiple authors, the run of John Campbell's "Astounding Science Fiction".
All of these were complete game-changers and redefined the genre or brought it to a wider popular audience. The Heinlein juveniles showed that it was possible to get away from horror and comic books in science fiction, and not talk down to the kids while doing so. Asimov completely redefined the way the robotics industry was viewed, even before there really *was* a robotics industry. Clarke was one of the first to depict aliens that were truly *alien* in their ways of living and thinking. And Campbell brought together great writers, gave them ideas to write *about*, and brought all that to the largest mass-market SF had ever had.
Asimov's Robots stories.
Arthur C. Clarke's 2001 and Rendezvous with Rama.
If you don't mind multiple authors, the run of John Campbell's "Astounding Science Fiction".
All of these were complete game-changers and redefined the genre or brought it to a wider popular audience. The Heinlein juveniles showed that it was possible to get away from horror and comic books in science fiction, and not talk down to the kids while doing so. Asimov completely redefined the way the robotics industry was viewed, even before there really *was* a robotics industry. Clarke was one of the first to depict aliens that were truly *alien* in their ways of living and thinking. And Campbell brought together great writers, gave them ideas to write *about*, and brought all that to the largest mass-market SF had ever had.