The Narnia books are geared for children but are some great writing anyway. You might try "The book of the dun cow" for some more adult good vs evil type fantasy reading. In it's original form it was part of a collection written by Irish monks in the early 1100s.
Book of Dun Cow is one of my favorites. Walter Wagerin (sp) has written several other fiction and non fiction Christian books.
Also his science fiction novels: "Out of the Silent Planet." etc.