Single volume Bible commentaries can be a useful resource. They require little shelf space, they can give a good summary of the text, and they can cost a lot less than a full set of Bible commentaries. I have profited from the following one volume Bible commentaries, but as stated on the home page of this site, I do not endorse everything that has been written by the respective authors.
Bible Knowledge Commentary (there is one volume for the Old Testament and one volume for the New Testament).
Baker Commentary on the Bible
The People’s New Testament With Notes by Johnson
Baker’s Dictionary of Theology (this is not a commentary in the typical sense of the word, but it does have much information on many Bible subjects).
The Liberty Bible Commentary
A New Testament Commentary by Howley, Bruce and Ellison
Irwin’s Bible commentary
Nave’s Topical Bible (while this book is not a commentary in the typical sense of the word, it does have much information on many Bible subjects).
The New Treasure of Scripture Knowledge (while this book is not a commentary in the typical sense of the word, it does have a lot of information on many Bible subjects).