The Ruins, by Scott Smith

My wife picked this book up in part because it was just released as a movie. As it turns out, it's an excellent novel, and not just within its horror genre. Sure it's creepy and has all the requisite elements for its genre. It's also an extremely well crafted and written book, though. The characters are touching, believable and deep, which, in the end, makes the book that much more frightening.