A question that I love to answer!
One book that I have read over and over and continue to read over and over is the Bible. It is important to my life.
Another book that I have found helpful is J Keith Miller's book A Hunger for Healing. In it he uses the 12 Steps of AA as a guide to help followers of Christ develop a more authentically honest and Biblical life.
A novelist that I have read over and over has been the late Morris West. He wrote three novels, The Shoes of the Fisherman, The Clowns of God, and Lazarus. They are all set in Italy of the 1960's and 1970's.
I am a bookworm and read a great deal (including a current project of a bio/autobio of every American President.)