Derek Kidner’s commentary on the Psalms, though too brief, is tremendous for its insight and elegance. Alec Motyer and Tremper Longman have also written great popular-level commentaries. Tremper’s volume is the best for helping you see every psalm as pointing to Christ. Eugene Peterson’s book Answering God is filled with great helps for understanding and praying the psalms. Peterson convinced me years ago I had to immerse myself deeply in the Psalms if I was going to know God.
You may also be interested in Tim Keller’s 9 Recommended Books on Culture