Below is a list of the most essential references for solid, expository and topical Bible study, grouped from most important to most optional. Within each group the listing is in no particular order, and every individual will have their own particular interests and circumstances. In every category, books should be selected with counsel from pastors or professors regarding the authors, and particular titles.
A good study Bible - Version should be KJV or NASB (1995) or ESV, by preference - but a good literal (formal equivalence) translation. Excellent study notes can be found in the Scofield or Ryrie Study Bibles, the Thompson Chain-Reference Bible, or the (Thomas Nelson) Open Bible, all of which are available using various translation versions.
An English Dictionary - I recommend Webster's Collegiate, but choose what you like.
A Strong's Exhaustive Concordance - A hard-copy version is much more useful than a digital copy.
A Conservative Bible Dictionary - I recommend Unger's Bible Dictionary, Smith's is also a good choice.
That's it. That's the foundation of a good Bible Study library - you need all of them, but you can get by very well with just these four books.
A copy of the Hymnal your church uses - I recommend you have one for planning purposes, and for personal devotion. If you start doing services or Bible studies outside of the church, you can easily find yourself leading a few songs - it helps to have a book.
Whole-Bible Commentaries by J. Vernon McGee and Matthew Henry are good for initial read-throughs, or for sanity-checking your thoughts on a passage. Both are conservative standards.
Nave's Topical Bible, this is useful for looking up topics where a particular key-word may miss some references. It is a reference which will help some, and will surprise you from time to time.
Systematic Theology - Lewis Sperry Chafer is best, Norman Geisler is also very good. Single-volume Theologies can be perfectly adequate and cost much less. Major Bible Themes by Chafer/Walvoord is excellent.
Vine's Expository Dictionary of Biblical Words - This is the standard companion to Strong's concordance, and adds depth of understanding for word-studies. It is not necessary, but can be nice.
Your Bookshelf is something that should grow as slowly as possible, as it can become immense if not restrained.
Your Bible-School Class Notebooks If you're lucky, your classes required you to turn in notebooks of your work and you still have them, and they're worth keeping - These can become VERY valuable in a dozen or more years!
Alternate Bible Versions - If you use KJV, make sure you have NKJV to compare wording to. If you use other versions you should have KJV, NASB, ESV, and may also want NKJV, ASV, and NIV - of value here is that some of these (KJV/NASB/NIV, etc.) are available as Parallel Bibles, allowing side-side comparison. This is of a little value in understanding passages, but really it's more important for checking your text in other versions, when you will be teaching a crowd who may be reading from anything - if their Bible says something different than yours, you want to know that. It is also very useful if you're witnessing to an individual who uses another version.
Whole-Bible Technical Commentary, I only recommend one set, and it is expensive - that's the Expositor's Bible Commentary by Frank E Gaebelein. The set is comprised of commentary by several authors, but the publication is done to a high standard, and helps unravel many of the more difficult passages. It must be seen to be appreciated, but I find it uniquely valuable.
Additional and Single-Topic Theology Works At the Desktop level, I recommend a single-volume Theology, such as Major Bible Themes by Chafer/Zuck, but for your Bookshelf a few multi-volume sets (Chafer's multi-volume) and various single-topic theology works will eventually become useful, depending on your depth of study and particular interests. Also, don't feel compelled to buy entire sets - I own 2 of Geisler's 4 volumes (v1 & v4), because those two had all the subjects I wanted more resource on.
Interlinear Bibles - Green's Interlinear is great your basic Greek and Hebrew using the Textus Receptus, while Brenton uses the Septuagint. Both are very useful classics, but certainly not for everybody.
NET Bible - The NET Bible is excellent for notes on translation considerations, at a verse-by-verse level. It is another reference which must be seen to be appreciated, but it is without peer in this regard.
Church History, especially Doctrinal History, can be of significant interest, especially as you study Systematic Theology. In the same category are Christian Biographies.
Biblical Period History and Archeology books can be of real value. Two highly recommended authors are F.F. Bruce and Randall Price. For those with $30/year worth of interest in this area, Biblical Archaelology Reviw (BAR) Magazine is still published and active online. My shelf also has a section on World History
Bible Outlines/Surveys/Handbooks - Seeing 'the Bible at a glance' can be very helpful. Proper interpretation of Scripture requires proper context, which in turn, requires a good perspective. I recommend the Wikinson & Boa Bible Handbook. Most any study Bible will have good outlines, but not all, and not as usefully presented as a book focused on Bible Outline will be.
Individual Bible Book Commentaries can provide a good mix of comfortable-reading commentary with additional information, but they are ususally application-based rather than overly technical/language-based. I like the Twenty-First Century Biblical Commentary Series by Mal Couch and Ed Hindson (various authors), but I know most of these authors, so I might be a little biased. It's a good, conservative series. Conservative classic authors include A.W. Pink, Warren Wiersbe, H.A. Ironside, and R.C. Sproul.
Individual Theological Subjects - Books are available on Inerrancy of Scripture, the Holy Spirit, Canon, End Times, and any other theological topic you can think of. The trick is selecting reliable authors - check with your church or your Bible institute.
Lectures to My Students, by Charles H Spurgeon - This book is disguised as a book on Homiletics, but is really an extaordinary read for anyone committed to the Ministry. Spurgeon talks about the Minister's spiritual and emotional needs in a frank, indisputable way which is beyond encouraging, as well as providing a lot of good, practical instruction for praying, preaching, and teaching.
Books on 'Doing Church' - There are books out there which outline weddings, funerals, etc., and books which tell you how to witness, disciple, and generally stay on track. The books I have in this category are no longer in print, but these types of books can be worth having (or not).
Books on Canon, Manuscripts, and Translations - For those with a deep interest in the origins and translations of our Bible, the resources are not as easy to find. Start with your seminary library, and expect to be hunting down out-of-print copies.
(See my Online Resources Page.)
Bible Gateway.com is the go-to online reference for searching and quoting Scriptures - simple, instant, and available in most any Bible version.
Extensive language references and tools, such as Logos Bible Software
Free Bibles/Tools programs (such as e-Sword) are great for accumulating free/cheap Bible versions and references, and then searching and using them together in side-side configuration.
Collections of older written material, usually in text or pdf format,
available through web sites or Bible software:
The writings of the Church Fathers and ancient historians
Commentary by people like Calvin or Wesley
Sermon collections