Adam Smith and the Virtues of Enlightenment (Cambridge 2009). A really helpful and sympathetic exegesis of Smith's Theory of Moral Sentiments, making it much easier to understand the rhetoric and organizational structure of Smith's great but neglected work.
Infrastructure: The Social Value of Shared Resources (Oxford 2012). A very important contribution to our economic understanding of infrastructure as a common or public good. The analysis is rigorous and compelling. As someone whose own work is primarily concerned with natural resources and environmental protection, I particularly enjoyed the chapter on "natural infrastructure." Those who are more interested in roads and bridges or telecommunications will find a great deal in the book that is useful to their work. Here's what Lin Ostrom had to say about the book:
Faculty and students across the social sciences and engineering will all find Brett Frischmann's new book to provide essential guidance for the analysis of diverse types of infrastructure resources and how policies affect the effectiveness, efficiency, fairness, and sustainability of outcomes. Rarely can one find such a broad and useful foundation for digging in and understanding the complexities of modern infrastructures. An extraordinary book.