Justified by Faith Alone by R.C. Sproul is a short little book, but packed with great insight and tight logic. It is written on a pretty high level of vocabulary, so I wouldn't recommend it to the person who is only casually interested in the subject. It is more like a college professor lecture than a devotional book written about faith. If you are looking for an academic look at the subject, you will not be disappointed.
The book is written as a recap of the struggle the reformers faced with the Roman Catholic Church. Although much of the book is rooted in historical arguments, Dr. Sproul mentions many contemporary issues that stem from the distinction evangelicals have in sola fide. It is not concerned with additional arguments, such as monergism vs synergism, so both Arminians and Calvinists would find it to represent their views.
Just over an hour in length, the audio is crisp and the narrator does a great job, even with the Latin phrases.
The christianaudio Reviewers Program (http://christianaudio.com) provided me with a copy of R.C. Sproul’s Justified By Faith Alone. My thoughts and opinions are my own.