The Whitefield books that were recommended are excellent for gaining insight and stirring up ones affection for ministry. It isn't just a biography on Whitefield. It also contains a host of other personalities that surrounded Whitefield such as the Wesley's, those involved with the Walsh revivals and the American revivals. It was a most edifying read. A Life by George Marsden on Edwards is a good read. McCrie's John Knox is excellent. Luther has some excellent biographies done on his life. John Owen has one done by Peter Toon that is good. J. I. Packer did one on J. C. Ryle that is very good called Faithfulness and Holiness. The John G. Paton book is a great read. Those are ones off the top of my head that I have read.