What Money Can't Buy: The Moral Limits of Markets by Michael Sandel. Very thought-provoking book by a Harvard professor. He discusses the evolution of the economics and economically-minded thinking into fields traditionally untouched by regular economists. For example, the concept of the incentive structure and influencing human behavior has been exploding recently, especially in management books and all sorts of things, but he highlights places where research has proven that this fails.
The more interesting parts of the book are where he discusses the use of economic incentives to solve problems: paying kids $2/book to up literacy rates in poor schools, paying people to be healthy to lower insurance rates, concierge doctors, and creating a market for organ transplants. He doesn't land on one-side or the other for any problem but rather acts like an journalist ethics professor that informs you about a given problem and provides different sides of the argument. Most of these problems are considered solved under the auspices of increasing economic efficiency, but even when the "market solution" doesn't fail, there is something missing, and he posits that economic solutions can sometimes corrupt and bastardize the thing that it is trying to solve. For example, say you pay a kid to read for the purposes of learning. Most people that read as adults do so for the intrinsic reward that it provides, but a kid that has been paid to read will replace that intrinsic reward with an external one and only read (and do other things that should be intrinsically motivated as part of our culture and society) when it benefits him externally.
It's not near as philosophical as I'm making it sound, but it is an easy read that questions the direction that our society is heading in the name of economic efficiency. As someone very interested in economics, this was a somewhat attitude adjusting read that helps reinforce that "don't take everything at face value" concept espoused by many on the site.