Christ Our Mediator by CJ Mahaney makes the gospel a matter of first importance. This short book is packed with challenges for every Christian. Most of us are familiar with images portraying Christ's death, but Mahaney says that it is only the preaching of the gospel, not the depiction, that God promises to accompany with saving effect. Christ or mediator (1 Timothy 2:5-6) had to bear the cup - that cup being the wrath of God for our sins - containing the full fierceness of God's holy wrath poured out against sin and intended for sinful man to drink. I think one of the biggest things that hit me as I was reading was that Christ had to experience abandonment of the Father, because He took on my sins.
In When the Darkness Will not Lift John Piper explains that any Christian can go through a period of depression and times when it seems like joy is out of reach. Piper uses examples in scripture and examples from other Christians to encourage believers as they fight for joy. I highly recommend this book and I, personally can't wait to read John Piper's When I Don't Desire God: How To Fight For Joy.
You can pre-order the book and find excerpts from When the Darkness Will Not Lift: Doing What We Can While We Wait For God - And Joy can be found at Good News and Crossway
A few years ago I read I Kissed Dating Goodbye and Boy Meets Girl so I was familiar with Joshua Harris and his honesty and upfrontness he shares in those two books. And again, I think Joshua Harris does a great job in this book of being upfront with us and honestly viewing lust as not just a sinful guy problem, but a sinful human problem. I think this would be great book for anyone struggling with lust, in any way, but also for those who aren't as aware of the lustful struggles that many men and women face.