This book by scholar Robert Alter has also been a tremendous resource to me while working on the songs for The Psalms Project. Alter tackles the text from a much more academic point of view as opposed to a faith-based Christian commentary, but I think it’s a valuable angle and perspective. For instance, his translations and interpretations are often more literally faithful to the Hebrew text, a little more “outside the box” of typical Bible translations, and he’s very forthright about some of the passages that are difficult to interpret due to copyists’ error or simple lack of scholarly information. He also translates the Psalms with a unique poetic sensibility that is refreshing. Here’s the book on Amazon, Barnes and Noble, and Google Books.