Strong's Concordance (contained in the Online Bible) [most any publisher]
                             or
Young's Concordance [most any publisher]

Wycliffe Bible Encyclopedia - 2 Volumes - [Moody Press, Chicago]

Vine's Expository Dictionary of Biblical Words by W. E. Vine - [Nelson Publisher, New York] 

Wuest Word Studies from the Greek New Testament - 3 Vol. by Kenneth S. Wuest [Eerdman's Publishing Co., Grand Rapids, MI]

Theological Wordbook of the Old Testament, by Harris, Archer, Waltke - Moody Press (for serious word study)

New Bible Dictionary edited by J.D. Douglas - [Inter-Varsity Press, Leicester, England & Tyndale House Publishers, Wheaton,IL]

Baker's Bible Atlas by Charles F. Pfeiffer - [ Baker Book House, Grand Rapids, MI]

A History of Israel - Davis, Whitcomb - [Baker Book House, Grand Rapids, MI]
                                                      and/or
A Survey of Israel's History, Leon Wood - [Zondervan Publishing House, Grand Rapids, MI]

Chafers' Systematic Theology (abridged) 2 Vol. - [Victor Books (if you find 8 volumes its better)

Manners & Customs of the Bible Times - Ralph Gower [Moody Press, Chicago]

A Harmony of the Gospels, A T Robertson is best (also contained in Online Bible)

The Crisis of Christ, G. C. Morgan - [Revell Publisher]

The Training of the Twelve, A. B. Bruce - [Keats Publisher]

Things to Come, Dwight Pentecost - [Zondervan Publisher, Grand Rapids, MI]

The Incomparable Christ, Oswald Sanders - [Moody Press, Chicago]

The Panorama of the Old Testament by Thomas R. Rodgers - [Impact Press, Box 382, Newburgh, Indiana 47629]

New Testament Survey by Gromacki - [Baker Books, Grand Rapids, MI]

Introduction to the Old Testament - R. K. Harrison, [Errdman's Publishing Co., Grand Rapids, MI]

Anything by A. W. Tozer

Treasury of David, C. H. Spurgeon - 2 or 3 Vol. [Nelson Publisher]

Mathew Henry's Commentary on the Bible (on Online Bible) [Revell Publisher] (contained in Online Bible)

Barnes Notes on the New Testament - 1 vol. [Kregel Publisher, Grand Rapids, MI]

The Greatness of the Kingdom by Alva McClain, [BMH Books, Winona Lake, IN] - A MUST! ! !

The Interpretation of Prophecy by Paul Tan, [BMH Books, Winona Lake, IN]

There Really Is A Difference by Renald Showers, [Friends of Israel, Bellmawr, New Jersey]

A History of Christianity by Kenneth Latourette - 2 vol. [Prince Press]