I have just finished reading the book A Shepherd Looks at Psalm 23 by Phillip Keller. I had read it before, but not for a long time. If you have not read it or have not read it recently, it is well worth your time to read.
From his years of experience as a shepherd, the author gives a lot of interesting background on Psalm 23, and also leads readers to a new appreciation of the tender care our Good Shepherd gives us.