There are zillions of Christian books out there, and many of them are worthwhile reads. There are few, however, that are truly outstanding. Here are some that really need to appear on your reading list!
Growing Spiritually:
1) The Spirit of the Disciplines, by Dallas Willard (author, Amazon)
2) Prayer, by Richard Foster (Amazon)
3) Life Together, by Dietrich Bonhoeffer (Amazon)
Understanding the Bible:
1) The Challenge of Jesus, by N.T. Wright (publisher, Amazon)
2) Slaves, Women, and Homosexuals, by William Webb (publisher, Amazon)
3) Surprised By The Power of the Spirit, by Jack Deere (author, Amazon)
Reasonable Answers to Honest Questions
1) Mere Christianity, by C. S. Lewis (author, Amazon)
2) Long Journey Home, by Os Guinness (Amazon)