Here is a list of some other good books by Lewis. I've read some of them myself, and there are some pretty good ones. Check them out.
Below are some other books I have read and would HIGHLY suggest reading.
A Family Guide To Narnia:
Biblical Truths in C.S. Lewis's The Chronicles of Narnia
The Discovery of Genesis
The Lord Of The Rings
Unlocking the Mysteries of Creation
Books by Karen Hancock:
The Light Of Eidon
Awesome book that may start out slow, but leads to a good ending and a fantastic sequal, The Shadow Within.
The Shadow Within
Possibly one of the best books I've ever read! If you love adventures and twists and turns around every bend, and love fantasy books, this is a book for you!