Thomas Watson was a Purtian non conformist in Civil War era England. He was a contemporary of John Bunyan. His book A Body of Divinity is one of the most easily read of all the works of the Puritans. In it he explains with a heart overflowing for love of Jesus Christ, the doctrines of the reformed faith. He uses as his outline the Westminster Shorter Catechism, but each chapter (which is actually a sermon) is delightful to read and wonderfully edifying.
I realize this blog is more geared towards works of fiction, but if you are looking for a good book to lift your spirits in devotion to the Lord, I highly recommend Thomas Watson's A Body of Divinity. It might be a little rough on younger teens, but really anyone with a heart for the Lord should be so taken with this book that it will be hard to put it down.
The book is currently published by Banner of Truth (http://banneroftruth.org), but you can also read a copy of it online at (http://www.iclnet.org/pub/resources/text/ipb-e/epl-10/web/watson-divinity.html)