C. S. Lewis
Finally finished a leisurely re-read of this classic. It is remarkably fresh - despite being around 50 years old (older, if you consider the source radio talks were during WWII) this book presents a sharp set of arguments for the Christian faith, as well as good advice and understanding of the life of faith and theology.
I need to buy a new copy someday - this one is tattered and falling apart. I treasure it though, so I'll not dispose of it. It was my father's copy (from my brother John, Christmas '67) and has his underlining and comments.