I've had several people (all Christians of course) recommend this book to me. One person commenting
on this book said that it "rationally explores the supernatural viewpoint". George Smith's book
does a good job of showing how this is impossible to do, but I will give Mr. Lewis a chance anyway
and put this on my 'to read' list.
Perhaps his most famous book is:
Mere Christianity for
which you can find a brief critique here by Dan Barker or a pro C.S. Lewis page here.