The Legal Theory Bookworm recommends The Practice of Principle: In Defence of a Pragmatist Approach to Legal Theory by Jules Coleman. Here is a description of this contemporary classic:
Jules Coleman, one of the world’s most influential philosophers of law here expounds his recent views on a range of important issues in legal theory. Coleman offers for the first time an explicit account of the pragmatist method that has long informed his work, and takes on the views of highly respected contemporaries such as Ronald Dworkin and Joseph Raz.
There are very few books that I believe should be read by every legal academic–this is one of them.