ChristianAudio.com is offering When I Don’t Desire God, by John Piper, as a free audiobook download through December 31, 2011.
To receive this audiobook for free, you will need to use coupon code DG1211 when you checkout.
According to the product description:
What do you do when you discover that you’re not satisfied in God the way he wants you to be? Joy is more than an afterthought of the Christian life; it is the sustaining fruit of a relationship with God. With a radical passion for Christ’s glory, John Piper helps you find the joy God wants you to have.
You can also download a free PDF version of the book from the Desiring God website.