Here are the two best books I've read on battling the sin of sexual temptation and temptation in general.
Joshua Harris,
SEX IS NOT THE PROBLEM (LUST IS)
I don't always like reading books specifically on the topic of lust because many well intentioned authors who are trying be transparent and frank are too descriptive and graphic in their anecdotes and examples which can take my mind places I never wanted it to go.
Harris' book is a clear and concise treatment of this subject that is rated PG. This book is filled with great advice for dealing with sin that is all centered around the gospel.
Kris Lundgaard,
THE ENEMY WITHIN
This book deals with the topic of sin in general and is actually based on a book written hundreds of years ago by John Owen called
The Mortification of the Flesh.
Why not pick up 2 copies of one of these titles and go through it with a friend or accountability partner. Harris' book has a study guide that you can buy separately and Lungaard has really helpful questions in the back.