I can only recommend what I've read, and of the sci fi books I've read, I would say these are the best. Also, if call yourself a sci fi fan, and you haven't read what's on my list, you really should, just so you understand what other sci fans are talking about when they say things like: "Walk without rhythm, and you won't attract the worm;" or "War is peace;" or "cyberspace".
[these are in order that I thought of them, and are not ranked in any way.]
1. Dune, Frank Herbert
2. 1984, George Orwell
3. The Time Machine, HG Wells
4. Neuromancer, William Gibson
5 Foundation Trilogy, Isaac Asimov
6. Martian Chronicles, Ray Bradbury
7. 20,000 Leagues Under the Sea, Jules Verne
8. Short story: "The Screwfly Solution", by Raccoona Sheldon aka Alice Sheldon
9. A Clockwork Orange, Anthony Burgess
10. Mary Shelley, Frankenstein
And making this list has reminded me to read some sci fi books that I've always meant to read, but never got around to reading, which are as follows:
1. Ubik, Philip K. ****
2. Ender's Game, Orson Scott Card
3. Do Androids Dream of Electric Sheep, Philip K. ****
And finally, I have to mention this one, which is technicallly a "children's book", but it's still great, especially if you are still under 18:
A Wrinkle in Time, Madeleine, L'Engle