I just started reading Dune.
The Dune books by Frank Herbert are my absolute favorite as far as Sci-Fi goes. For a guy who never graduated college he is a freaking genius of a writer. All the different things- philosophies, religion, politics and technology that he wove into these books with a masterful storyline is simply amazing. Hope you like reading them.
The sequel and prequel books by his son and Kevin Anderson aren't on the same level but good reads also.
Awesome response people- keep it up with all the great suggestions and discussions.