C.S.Lewis wrote Screwtape Letters,
Very interesting stuff.
I have read several of his books.
I should read more and lose this
dumb phone.
My favorite three are the Great Divorce, Abolition of Man, and Pilgrim's Regress, but I like them all (I mean his books for adults, not so much Narnia). Mircales and The Problem of Pain are great if you are into apologetics. Warning about Pilgrim's Regress...its a weird one, first book he wrote since becoming a Christian I think, and he was a bit less charitable in it than his others.