Rob Smith asked in a comment, "What are the 5 books I must read, excluding the Bible (too obvious)?"
I think this is an impossible task. Having not given this any thought, here goes a try, not in any order.
1. CS Lewis -- Mere Christianity -- Lewis firms up basic belief with reasonably thoughtful and deep analysis, all the while being very gracious.
2. Dietrich Bonhoeffer -- The Cost of Discipleship -- the heart of Christian discipleship.
3. Peter Kreeft -- Christianity for Modern Pagans - a dialogue with Pascal about his Penses.
4. Brian McLaren -- The Story We Find Ourselves In: Further Adventures of a New Kind of Christian -- this is the second in a fictional trilogy, and I'm not saying read it for theological reasons. Read it watching the encounter between followers of Christ and non-followers to see what their real questions are. You can read the whole trilogy, but I found the second to be the best, and I promise you won't be lost if just read the second.
5. I can't think of a # 5 off the top of my head.
Some other interesting books -- Aqua Church by Leonard Sweet, The Journey: A Spiritual Roadmap for Modern Pilgrims by Kreeft, ...
I've tried to be very sparing here. Please, others suggest a couple of must reads. All of mine are Christian based, but that doesn't mean those are the only must reads.
I might add A Short History of Nearly Everything by Bill Bryson. My brother is really loving Freakonomics right now.