A New Reading Challenge

I've got to be honest. Until the last few years, I had never read more of C. S. Lewis's works than the Chronicles of Narnia. They hadn't even crossed my radar. However, due to the reading challenge I was doing with some friends over the last few years, I've read a couple of books, one of his and one about him, that has left me intrigued more than ever.
Two years ago I read Mere Christianity, expecting it to be over my head. It wasn't. Perhaps because I had read quite a few other books written by British authors, the text was very easy for me to pick up, and I found myself giggling at the way he put some things while also going, "huh." That's a great point.
Last year, I read Becoming Mrs. Lewis, which is a fiction piece based on the true story of how C. S. Lewis met his wife and eventually married her. It's written from her perspective and opened my eyes to a ton of things I had never considered, due to him being one of the most acclaimed Christian authors ever. It's not that anything bad necessarily happened between them. It just wasn't what I had expected.
Anyway, all that to say, I've decided to give myself an additional reading challenge this year. I plan to try and read one of Lewis's books each month this year. I started in January with A Grief Observed, which is his journal from right after his wife passed away. Once again, not what I expected, and in some ways, so much more.
I'm not sure what I'll do each month for the rest of the year, but I'll give you an update at the end of the year. I might even try out his space trilogy. Did you know he wrote one?
Have you read many of his books? Which ones are you most interested in? Do you have an author you'd be willing to read one of his or her books each month for a whole year?