Here, in no particular order, are some of my favorite books related (perhaps indirectly) to the Protestant Reformation:
The Consuming Fire by Michael Reeves
This is my favorite introduction to the Reformation. It is rich in historical detail and theological reflection. Highly Recommended.
Living For God's Glory by Joel Beeke
The contributors of this wonderful book trace the history of the Reformed faith exploring its key doctrines, such as the Doctrines of Grace and the five solas of the Reformation. This volume is rich in devotional appeal as well; exploring Reformed piety and worship.
The Grace of Godliness by Matthew Barrett
Without a doubt, Matthew Barrett's book is one of the best explanations of the Doctrines of Grace. He traces the historical background of the Canons of Dort and demonstrates the biblical justification for the Doctrines of Grace. But this book is also an exercise in theology as doxology. A must read.
Here I Stand by Roland Baintan
The classic biography of Martin Luther.
Reformation: Yesterday, Today, and Tomorrow by Carl Trueman
Dr. Trueman traces the lasting significance of the Reformation for the church today. Required reading.
Chosen For Life by Sam Storms
Outstanding explanation and biblical defense of the doctrine of unconditional election.
God Has Spoken by J.I. Packer
The Reformation was a Word-driven movement. You cannot understand the Reformation if you do not have an adequate understanding of the doctrine of Scripture. This little volume by J.I. Packer is one of the best introductions to the authority and sufficiency of Scripture.
A Quest For Godliness by J.I. Packer
In this excellent book, J.I. Packer examines the lives and piety of the Puritans. This is my favorite introduction to the Puritans, their theology, and their approach to Christian living.