"Baker's Encyclopedia of Chrisitian Apologetics" by Norman L Geisler. Apologetics (not apologetic or apologizing because of an error, it is a branch of study devoted to the defense of the faith). Geisler has an amazing way of putting things into words and writing with a lot of simplicity and helpful charts. If you are interested in finding answers to perplexing questions about the Christian faith then this is a book you may want to consult. Also he writes about some of the men that have been most influential in the medieval and modern Christian era. 1 Volume, and 841 pages of good stuff no doubt. Since the prolifiration of books on CD, Geisler's complete work on Apologetics is also available somewhere out there in cyberspace or your nearest "Christian" Bookstore. That one contains a boat load of his other writings - but that is beyond the scope of this blog thread.
Click on this link to see previously recommended books.