These are extremely helpful single-volume resources. If you're building a biblical studies library, you'd do well to start with these.

It's always preferable to read several different commentaries on each book, gaining the benefit of diverse perspectives on the subject. If we had to pick just one useful commentary for each book, here's a list.

Again, we'd really prefer to provide a range of commentaries for each book, but given our self-imposed constraint of one recommendation per book, here's our (rather idiosyncratic) list.

Commentaries often come in series, with a group of editors/authors working with a particular interpretive structure. Here are some series that are generally of excellent quality.