When I first started reading science fiction, there were acknowledged classics that everybody read: The World of Null A, the Foundation Trilogy, Heinlein's Future History, The City and the Stars. Today, because there are so many more books and writers, it is much harder for a book to earn that kind of recognition. Dune, of course, but that was a long time ago. Ender's Game also quite a few years ago.
Of modern books, I'd say Perdido Street Station is one of the half-dozen whose name keeps coming up. I haven't read it yet, but it is high on my list.