I second The Diving Bell and the Butterfly. Amazing read.
I'm surprised no one has mentioned Complications: A Surgeon's Notes on an Imperfect Science. This book should be required reading for all premeds.
The next book on my list is The Lost Art of Healing: Practicing Compassion in Medicine.
Other nonfiction I've enjoyed in recent years:
Stiff: The Curious Lives of Cadavers
Nickel and Dimed: On (Not) Getting By in America
Fast Food Nation: The Dark Side of the All-American Meal
Eat, Drink, and Be Healthy: The Harvard Medical School Guide to Healthy Eating
As Nature Made Him: The Boy Who Was Raised as a Girl
Genie: a Scientific Tragedy
Guns, Germs, and Steel: The Fates of Human Societies
The Demon-Haunted World: Science as a Candle in the Dark
Why We Get Sick: The New Science of Darwinian Medicine
The Moral Animal: Why We Are, the Way We Are: The New Science of Evolutionary Psychology