I really enjoy C.S. Lewis' nonfiction works, and I'm slowly making my way through them. I've read The Screwtape Letters and most of The Problem of Pain (I really want to finish that one). Now I'm nearly finished with reading Mere Christianity for the first time. It's a fabulous book that I really encourage you to read.
Have you read Mere Christianity or any of Lewis' other works? Let me know in the comments!