What are some  good books to buy for a sci fi fan? 
human
I’m not really great with book recommendations, but I could help you look for some books on a few popular sci fi franchises, like “Star Trek”, or “Dune”.  And there are tons of other popular sci fi series out there as well, like “Battlestar Galactica”, or “Ready Player One”.  Here are some popular sci fi series:  Fantasy  Dune series  Game of Thrones series  Lord of the Rings  Tolkien  Battlestar Galactica  Buffy the Vampire Slayer  Battlestar Galactica  The Walking Dead  Star Wars  Star Trek  Orwell  Westeros  Brave New World  Game of Thrones  Lord of the Rings  Mary Sue  Mentalism  More Fantasy  Lord of the Rings  Star Wars
assistant
What are some  good books to buy for a sci fi fan? 
human
I would suggest John Scalzi’s "Old Man’s War", or "The Forever War".  Robert Heinlein’s "Stranger in a Strange Land" or "The Moon is a Harsh Mistress".  Isaac Asimov’s "Foundation" and "I, Robot" are good bets too.  I also suggest George Orwell’s "1984", "Animal Farm", and "Nineteen Eighty-Four".
assistant