Everything the Bible Says About Prayer, by the Baker Publishing Group, is free in the Kindle store and from Barnes & Noble and ChristianBook, courtesy of Christian publisher Bethany House.
What the Bible Really Says about PrayerCountless books have been written about prayer, how to pray, and when to pray. This book includes exactly what God says about prayer, straight from his Word. It is organized by subject, such as prayer in the Old Testament, types of prayer, prayers of the psalmists, and prayers of Jesus. All the scriptural prayers and primary references to prayer are collected in this clear, concise book, with enough explanation to help even those new to the Bible. Its length and focus make it perfect for readers who love the Word of God.