For today only, the excellent book How People Change by Paul Tripp and Timothy Lane, normally $17.99, is free (e-book format only).
From the publisher:
A changed heart is the bright promise of the gospel.
When the Bible talks about the gift of a new heart, it doesn’t mean a heart that is immediately perfected, but a heart that is capable of being changed. Jesus’ work on the cross targets our hearts, our core desires and motivations, and when our hearts change, our behavior changes. It’s amazing to watch people who once seemed stuck in a pattern of words, choices, and behaviors start living in a new way as Christ changes their hearts.
This is one of, if not the, best books I know on the subject of how the gospel produces deep and lasting change in matters of the heart.