I have recently been doing a paper for my Biblical Theology class on prayer throughout the Old and New Testaments. One of the best resources that I have used is Graeme Goldsworthy's Prayer and the Knowledge of God: What the Whole Bible Teaches. Goldsworthy gives an overview of the theology of prayer and then traces the prayers of the prophets, priests, and kings along with the teachings of the New Testament. I would highly recommend this book for academic research or just devotional reading.
