For a number of years the Seminary faculty has produced the Basic Library Booklist. It is updated every few years, and you can find the 2014 edition here. The Booklist has been specifically designed to answer the question of which books are the best on a particular book of the Bible or theological subject. In the case of commentaries, best means those that are the most helpful in exegesis and exposition, as well as understanding the overall argument of a book. The books are listed in order of importance. The first book listed is the one that should probably be purchased first, though it is doubtful that one commentary would be sufficient for adequate sermon preparation.
Besides commentaries the Booklist also rates books in systematic theology, historical theology, and practical theology. Check out the Booklist and let us know what you think.