Favorite Lewis books

Mere Christianity is his best known and, having read it again 20 years after the first time, I can honestly say it's great and that I got more out of it the second time. His memoir Surprised By Joy was not at all what I thought it would be, yet it was a wonderful piece of intellectual autobiography. Finally I recently came across some rare but interesting essays at the library, collected under the title Present Concerns (1986). I confess that I have never read The Screwtape Letters. I read the Space Trilogy and hope to go back to it. I have not read Narnia simply because fantasy is not my favorite genre. Interested to see what other people recommend. Thanks.

If you are prepared to swallow enough "fantasy" to read the Space trilogy, then you could perhaps try Till We Have Faces, which is a historical novel set in a non-existent country.

I second that Till We Have Faces is definitely my favorite.

Till we have faces is a great book - though I must admit I still don't think i've really understood it. For sheer power, however, I rate The Screwtape letters, and I think this is far and away his best theological work - mainly because he was a far better writer of fiction than a theologian. This and A grief observed show Lewis at his best as an honest and compassionate observer of human nature.
To understand the man, however, I think you must read The discarded image, which is the heart of his 'real' work - his professional life as a professor of English Literature.

4> For the same reasons I also liked The Great Divorce.

Yes, I love that too - Lewis has a great gift for writing scenes that are so true to human nature that they stick in the mind, and many of his best are in The great divorce
Though, really, Narnia says all he has to say about God and Christianity, and says it brilliantly because he's using the genre he loved the best. (I wrote my undergraduate dissertation on this!)