The one-volume New Bible Commentary, 4th ed. (InterVarsity) is excellent, as is the two-volume Zondervan NIV Bible Commentary (Zondervan).

Bible Dictionaries:

I have frequently used the New Bible Dictionary,  2nd ed. (InterVarsity) but would also recommendThe New International Dictionary of the Bible (Zondervan).

Bible Atlases:

I would suggest The Zondervan NIV Atlas of the Bible (Zondervan), and A Visual Guide to Bible Events (Baker).

Books on Bible Study:

Two of my favorites are How to Read the Bible for All Its Worth, by Gordon Fee and Douglas Stewart (G. K.Hall) and Living by the Book, by Howard Hendricksand William D. Hendricks (Moody).