Rendezvous with Rama by (Sir) Arthur C. Clarke was my first proper introduction to the written word of science fiction. And there are few better books to hook you in good and proper.
"Opowiadania" by Stanislaw Lem (author of Solaris)
The Number of the Beast by Robert A. Heinlein, i had some trouble gettimg my head around some of the concepts and to some degree still do, but it was a good read.
"The Forever War" 1974 by Joe Haldeman. Very different from your usual space based novel. I still recommend it.
Starship Troopers
