John Pollock (above) is my favourite Christian biographer.
You can pick up his biography of the Apostle Paul for free (US/UK Amazon Kindle). Wilberforce is just $1.99 or £0.99.
UPDATE: While you’re there the New American Commentaries are still 90% off. For those who don’t own a Kindle device, you can still load the Kindle app onto your Mac/PC/iPad/device.
Never buy a book at full price (unless it’s mine).