Nancy Farmer's House of the Scorpion. In a future where the druglords have founded their own country on the Mexican-U.S. border, a young boy growing up on the luxurious estate of one of the notorious El Patron learns that he is a clone . . . and that El Patron will harvest him for organs when his own 140-year-old heart finally fails. Thrilling, chilling, and even better than her wonderful The Ear, The Eye, and the Arm, which I also recommend.
Oh, and hey, I just Logan's Run last night. I haven't seen that since I was a kid. Strange, I don't remember it being quite so incomprehensible and full of boobies. But I think it's a must-see for sci fi fans, it's one of those classic stories that gets referred to and spoofed all the time. Also, the heroine's name is Jessica. Can't go wrong there!