I'm not a fan of books that fall into the "Christian self-help" category. Below are some great books if you want to grow in your understanding of who God is and what He's done for you. One of the thing's that truly defines the Christian culture is the necessity of our growth in the love for the written word. Scripture sits atop the list of books we need to truly grow, but I've found that some of the books I listed helped me understand the Bible better.
Knowing God - J.I. Packer
It's just my personal opinion, but J.I. is as good as they get. If you want to read someone expound on the attributes of God to the point that it sounds like they were roommates in college, then you're looking for this book. It kept me awake for hours after I'd put it down. I had to go back and read it again recently. I said these were listed in no particular order, but I put this one on top for a reason.
Knowing God - On Amazon
R.C. Sproul's Crucial Questions Series
R.C. put together a great series of really short, but detailed books on very important aspects of the Christian faith. They are short and most can be read in a day, so there's really no excuse for everyone not to read through these. You can't use cost as an excuse either since they're all free in eBook format. R.C. always does his best to combat one of the biggest problems facing the church today, anti-intellectualism. Local book stores are filled with self-help books. Local Christian book stores are filled with self-help books with Bible verses in them. You won't find any tips on money management or being a more "radical" Christian from Dr. Sproul. Subjects include baptism, prayer, Jesus, and assurance of salvation. Don't pass these up.
R.C. Sproul's Crucial Questions series from Ligonier Ministries
Lectures on Calvinism - Abraham Kuyper
A great series of lectures on the Reformed faith pulled from six different lectures that Kuyper did at Princeton in 1898. The lectures were on Calvinism as a Life-System, Calvinism and Religion, Calvinism and Politics, Calvinism and Science, Calvinism and Art, Calvinism and the Future. Kuyper does a great job of plugging in this theological system into various aspects of everyday life. Hopefully it can be useful to show people that there's more to discuss than just the TULIP.
Lectures on Calvinism - On Amazon
The Prodigal God - Tim Keller
Keller always does a great job of putting the Gospel on full display in nearly every parable or segment of scripture. I think most people see this story as one of licentiousness on the part of the younger son, but Keller examines the father and older brother to show us that we are all both "older brothers" or "prodigal sons" at some point in our lives. This is a great examination the legalist in all of us.
The Prodigal God - On Amazon
Institutes of the Christian Religion - John Calvin
I don't think any brief review of mine would do this justice. Next to the Bible itself, no book has taught me more. You don't have to be a Calvinist to appreciate Calvin himself. This book will destroy any part of you that you think is good in the eyes of God, and forces you to see the Gospel as the only possible way to please God. I'm not that sure what Calvin himself would think of TULIP, but I'm 100% sure he would think we got the 'T' right.
Institutes of the Christian Religion - On Amazon
The Explicit Gospel - Matt Chandler
Chandler has a way of delivering the Gospel to people in my generation that cannot be matched. Most people like him because he's funny, but the humor really helps you tie the facts back to the jokes so you'll remember them long after you're done reading. On a side note, I highly recommend Chandler to anyone that's looking for a good podcast.
The Explicit Gospel - On Amazon
Sola Fide: The Reformed Doctrine of Justification - J.I. Packer
This is just a short essay from Packer, but he puts as much in 20 pages as most authors do in 300. Only available in kindle format.
Sola Fide: The Reformed Doctrine of Justification - On Amazon
Through the Eyes of C.H. Spurgeon: Quotes From A Reformed
Baptist Preacher - McCaskell
Great quotes pulled from sermon excerpts of the great C.H. Spurgeon. The quotes have been organized according to topic and also include the original sermon title.
Through the Eyes of C.H. Spurgeon: Quotes From A Reformed Baptist Preacher - On Amazon
Anything written by C.S. Lewis
I doubt much detail is needed here. 'Mere Christianity' is worth the cost of the set alone. C.S. is still considered one of the greatest Christian apologists ever. Before reading his work I would highly suggest digging up a little of his background information and testimony. His conversion to Christianity makes his work all the more brilliant.
The Complete C.S. Lewis Signature Classics - On Amazon
An Introduction to Covenant Theology - J.I. Packer
I guess you're starting to see a theme here. In case I haven't made it clear enough, I'm sort of a J.I. Packer fan. This is another in a series of essays from Packer that's only available in Kindle format. It's a great exposition on the covenant relationship between God and His elect. To pull a quote directly from this essay as to why understanding this covenant relationship is so important; "the Word of God is not properly understood till it is viewed within a covenantal frame."
An Introduction to Covenant Theology - On Amazon
The Joy of Calvinism: Knowing God's Personal, Unconditional, Irresistible, Unbreakable Love - Greg Forster
If you want to learn more about the mechanics of salvation, this is a great read. While some people think this is an unimportant debate, I feel like it changes everything about the way you worship and live. Having a man-centered view of salvation puts you in a position of doubt or sometimes self-righteousness. Having a God-centered view of salvation keeps you comfortable as you live out your life and allows you to be more humble as you remove yourself from the process. This book really helps you understand how God saved you personally instead of just creating a system of salvation that you're allowed to participate in if you choose. I highly recommend this one.
The Joy of Calvinism - On Amazon