Top of my list:
His Dark Materials trilogy by Philip Pullman
Though origionally sold as a children's book in the UK, it is now widely recognised as a book to be enjoyed on all different levels. The author calls it fantasy-realism and it's a must. In fact, I'd be shocked stunned and deeply disturbed if you haven't heard of it as it's supposed to be pretty widely marketed in the US, though I gather with a smaller following than in the UK.
The Alchemist by Paulo Coelho
This is probably quite a well known book but is nevertheless very good. It explores ideas about philosophy and spirituality in the form of a fable - very thought provoking. I also recommend some of his other books such as The Devil and Miss Prym and Manual of the Warrior of Light.
The Life of Pi by Yan Martel
This book was the winner of the Booker Prize this year in the UK. It's quite interesting, again going into ideas of philosophy and religion but also a darn good adventure story, about a boy who becomes stranded on a lifeboat with a Bengal tiger. I think for some it may take a bit of getting in to but I soon found it hard to put down.
