Can I vote for Contact by Carl Sagan here as well?? If it's the best movie, it must be the best book, right? Of course, I read it when I was a teenager, so I have no idea what it was really like. I'll have to admit to not having read a lot of sci-fi novels, but those that do stick out in my head are those of Ursula K. Le Guin (The Lathe of Heaven, Left Hand of Darkness) and although she is not a sci-fi author, Margaret Atwood (The Handmaiden's Tale).
I've tried to read some Phillip K. Dick but I have not been able to stick with him. I have yet to finish one of his novels.