Ravi Zacharias: Can Man Live Without God?
An amazing book that makes the case for God not by citing the Bible or great theologians, but by analyzing the philosophies of famous atheists and showing their flaws.
C. S. Lewis: Mere Christianity
C.S. Lewis was an atheist for much of his life. Appropriately, this book makes the case for the existance of God first and Christianity second with carefully outlined and surprisingly simple reasoning. I consider this required reading for anyone searching for meaning.
C. S. Lewis: Space Trilogy
Religious Sci-Fi Fantasy: A very tiny genre. In "Out of the Silent Planet", "Perelandra", and "That Hiddeous Strength", C.S. Lewis manages to tackle difficult theological questions as we follow Dr. Ransom in his adventures on Mars, Venus, and back on Earth. My favorite science fiction series by far.