Any time you encounter a term or idea you are not familiar with, pick up this handy little reference. Yes, it does fit in your pocket. It's also useful simply to read from beginning to end if you are new to the subject of apologetics or philosophy of religion.
This is a massive tome by Norman L. Geisler which is quite comprehensive in its scope. If there's an issue that has been encountered in apologetics, then it is probably going to be outlined pretty thoroughly here. Very useful for getting an overview of a topic, a key thinker, or an argument.
There's no better all-in-one apologetics textbook than this recent work by Douglas Groothuis. Useful for chapter-by-chapter study, quick reference, as well as for creating teaching outlines and exploring the cumulative case for Christianity. Get this book; read; repeat.
The Apologetics Study Bible
This study Bible includes detailed notes from an apologetic perspective. Run into a scriptural issue that you need input on? Check it out in the Apologetics Study Bible. It also includes historical vignettes of major apologetic personalities, short articles on various apologetic arguments, and input from a wide array of scholars on pertinent contemporary issues in apologetics. Worth having as a Bible, if not just for reference.
Holman Quicksource Guide to Christian Apologetics
This unique illustrated guidebook is a visually helpful overview and outline of the major issues in Christian apologetics. This is also a great book for the beginner to get his/her hands on in order to get a good bird's-eye-view of the apologetic landscape, so to speak. This can also be very useful as a tool for preparing apologetics talks, as it covers a broad amount of key content and includes many good examples.
New Dictionary of Christian Apologetics
This is a large book, similar to the Baker Encyclopedia mentioned above. However, the main difference is this one has a large variety of scholarly contributions. Part one is a series of essays on apologetic topics, followed by part two -- a dictionary of apologetic issues, historical figures, and concepts. A great reference tool.
Pocket Dictionary of Theological Terms
Again, another handy dictionary for the apologist - this one focusing on theological terms. About the same size as the Pocket Dictionary listed above, but much denser, this little book is also useful for reference as well as reading all the way through to discover all those terms you've never heard or understood before. Get both and use them.
Encyclopedia of Bible Difficulties
This is a dense book packed with answers, angles, and analysis of all the major Bible "difficulties." What it gives you is a good, scholarly treatment of scriptural passages that may not be easy to reconcile without a bit of study and further understanding. This is a good reference book to have on hand if you encounter these sorts of objections regularly.
Faith Has Its Reasons
One of the best books covering the various schools of thought in apologetics. This must-read book by Ken Boa and Rob Bowman clearly unpacks the various apologetic methods, showing their logic, strengths, and possible weaknesses. For the apologetics student, this would serve as a good companion to the Groothuis textbook mentioned above.
Philosophical Foundations for a Christian Worldview
Anyone who has read this book has surely been changed by it. Not only is Craig and Moreland's phenomenal philosophy textbook is a must-read, it's also a very useful reference. Worth going back to and stacks up nicely next to the other heavy reference books!
What books are on your shelf that continue to be a regular reference to you as an apologist? What do you think is missing from this list?