some SF reccomendations
Well it really depends on what sort of a read you are looking for, but I'll list a few of my favourites in any case.
The Dune series is definitely a classic, but after the first volume it can get a bit too involved and dispersed over time for some. In any case, I suggest you stick to Frank Herbert's originals and avoid the prequels which have no real character to them, IMO.
Isaac Asimov - The Gods Themselves. Asimov considered this one of his best novels, in particular because he considered the section where he describes an alien social structure in detail to be a case of him writing over his own head! Continues to be one of his most thought-provoking novels.
Arthur C Clarke - Rendezvous with Rama. The rest of the series varies, but this is real mind-expanding hard SF at its best.
James Blish - A Case of Conscience. Considers some theological implications of alien life, very thought provoking.
David Zindell - Neverness. Beautifully wirtten and crammed with ideas that willsend your head spinning.
Ursula le Guin - The Left hand of darkness
One of the most vividly imagined alien societies ever.
Robert Silverberg - Nightwings
One of the best-realised future-earths ever.
AE van Vogt - The World of Null-A
A baffling, obtuse but very rewarding piece.
William Gibson - Neuromancer - The book that spakred cyberpunk and gave SF a much-needed shot in the arm
Other authors to look out for are Phillip K Dick, Robert Heinlein, Ray Bradbury, Ken MacLeod, Jack Vance, Bruce Sterling, Larry Niven, Brian Aldiss...I could go on all day.