Ray Pritchard links to some fairly extensive lists of Christian books online, a few of which I'm very glad to recommend. You can browse through yourself to see the comprehensiveness of what's now online.
F.F. Bruce's The Historical Reliability of the New Testament is the first comparison I know of between the New Testament documents and other literature at the same time, concluding that the standards classicists use for determining authenticity make the New Testament come out as the most likely to be authentic of any ancient documents (where authenticity isn't about the proof of all its content but the reliability of its transmission and the origin in the general time period and setting it claims to be from and therefore its value as a source about early Christianity).
Two works by Jonathan Edwards come with my strongest recommendations. On the Freedom of the Will played a large part in my early thinking on the issue (though my views as they stand are much more informed by contemporary philosophical debate and D.A. Carson's Divine Sovereignty and Human Responsibility, the best treatment of the Bible (and intertestamental literature) on this issue that I've seen, and R.C. Sproul's Chosen By God was the first work besides the Bible that got me thinking explicitly along these lines).
The other work by Edwards that I recommend highly is A Treatise Concerning the Religious Affections, which came out of his reflections on the Great Awakening and all the spurious conversions amist the genuine ones. His distinction between the two relies on what he calls religious affections, which you might think of as somewhere between what we nowadays call the mind and the heart and include the fruit of the Spirit. A genuine conversion involves a transformation of these religious affections. This is the classic work on that sort of issue.
John Calvin's Institutes on the Christian Religion is a masterpiece of systematic theology, and he doesn't even really get to the doctrines that eventually became labeled Calvinism until the end. Also, all of Calvin's commentaries are online now.
Finally, I'll link to John Piper and Wayne Grudem's Recovering Biblical Manhood and Womanhood, though it's with some hesitation. I'm not happy with most of what's been published on this subject, and the stuff I like a lot is mostly at the academic level and not very readable to the average Christian. I've got mixed feelings about this book. The exegetical and theological section is very good, at least most of the chapters (each is by someone different). The introductory stuff is sometimes good but at a number of points makes me cringe, since it doesn't represent very well the position that I think is biblical. I haven't looked at most of the second half of the book, but I suspect some of it is good and some not. My favorite book on the subject is out-of-print, and the contributions by Craig Blomberg and Thomas Shreiner to this book are also very good. Craig Keener and Linda Bellville also have chapters in that book, and they're top-notch biblical scholars who probably best represent the view I disagree with. Anything else I would recommend is either only in scholarly journals or in a technical enough anthology that I wouldn't recommend it to most readers of this blog. I do plan to post on this subject soon, so I'll probably say some more specific things about the literature on the topic then.