Books with a unique concept

I love a book with a unique concept. This year I read a book called "www.wake" that had the concept of the internet itself becoming self aware, a book called "Parasite" about a society that uses genetically-modified tapeworms as health improvement until the tapeworms start taking over, and "Micro" by Michael Crichton where people are shrunk to less than the size of an ant and kill people basically from the inside out.

I would love a recommendation for a book with a unique, interesting concept; one that ideally isn't too hard to grasp. Fantasy or sci-fi are both fine.