The Fall and Sin
'I have spilt his precious blood, trampled on the Son of God'
The Bondage of the Will
Luther's as rude as ever. This book will change your life. Read the forward by Packer- perhaps the best thing he's ever written.
Institutes of the Christian Religion, Book II
It don't come better than this!
The Theology of Martin Luther
Don't be deceived by the title- it's not relevant only for looking at Luther. Few books are more powerful on sin.
On the Mortification of Sin
The richest of soul feasts.