Brave New World and Stranger In A Strange World are excellent suggestions. They are among the ten sci-fi books that have defined the genre.
To those two, I would add Dune. Forget the movie. The book is absolutely amazing. It has been selected the Best Sci-Fi book of all time in pretty much every poll on the subject.
motherpi - I agree with your DH. Hyperion is indeed brilliant.
These are all "old school" sci-fi - space ships, alien races, etc. For something a bit more modern (computers, information age, hacking, etc) Neal Stephenson is... GOD. No really. His Snow Crash and Diamond Age are quite incredibly brilliant. Cryptonomicon is my favourite but would be too much for a book club choice.
In comparison to the above, Iain Banks books are rather shallow, simplistic, and not really credible. And they are all the same. Player Of Games was OK, although nothing to rave about. The Go games in Shibumi were more engaging and intellectual, I thought.