My all-time favorite book on forgiveness is Total Forgiveness by RT Kendall. His book is so clear and concise in getting to the bottom of our resistance to forgive. He clearly lays out what forgiveness looks like and how we should act towards a person we have forgiven.
There are other books out there that deal with forgiveness. Here are a few that I have found helpful.
Prayer of Revenge: Forgiveness in the Face of Injustice-This book talks about impeccatory prayers as a step in forgiveness.
Free to Forgive-This is actually a Bible study
The Peacemaker: A Biblical Guide to Resolving Personal Conflict-This book is not only on forgiveness, but conflict resolution