Recommended reading on Prayer

A number of friends I respect highly recommended a good book in prayer, entitled "A Praying Life" by Paul E. Miller (NavPress). I've just about finished the book myself now, and I agree that it's probably the best book on prayer and praying that I've ever read. It's a highly practical book, both convicting and encouraging, and you can tell that wise theology lies beneath the surface of the very life-related teaching and examples the fill the book.