Douglas Irwin – Free Trade Under Fire, 4th Edition
Excellent, except for the carbon tax proposal at the very end. Knowledge problems and incentive problems doom that idea. Otherwise, while a bit long for an introductory text, this book is about as good an intro to arguments for and against free trade as there is. It is also a good guide to institutions such as the WTO and the recent move towards multilateral, bilateral, and regional trade agreements.
Inertia Wins! 