I love Narnia! I also enjoyed the Screwtape Letters. I used the Screwtape Letters with my 7th grade Confirmation kids. They really understood it.
Newer editions are bound with "Screwtape proposes a toast" which is Lewis' take on public education. Everything he said has come true . . . .
I SEEMED to be standing in a bus queue by the side of a long, mean street. Evening was just closing in and it was raining. I had been wandering for hours in similar mean streets, always in the rain and always in evening twilight. Time seemed to have paused on that dismal moment when only a few shops have lit up and it is not yet dark enough for their windows to look cheering. And just as the evening never advanced to night, so my walking had never brought me to the better parts of the town. However far I went I found only dingy lodging houses, small tobacconists, hoardings from which posters hung in rags, windowless warehouses, goods stations without trains, and bookshops of the sort that sell The Works of Aristotle. I never met anyone. But for the little crowd at the bus stop, the whole town seemed to be empty. I think that was why I attached myself to the queue.
Online here: The Great Divorce
If you liked Screwtape check out Peter Kreeft's "Snakebite letters." He did an updated version of "Screwtape" dealing with some contemporary issues and it is almost as good as Lewis.