You won't sit down and read this one cover-to-cover (well, I doubt it) but James L Mays' commentary on the Psalms in the Interpretation Bible Commentary series is a stunner. He seldom fails to be deeply stimulating, is always reverential and is a great addition to any preacher's books on the psalms. From a Lutheran background, you'll also find his liturgical connections helpful and he always brings us to Jesus.
There are few commentaries I rate as highly as this one. And you can even try it out via Google Books! Tremper Longman III gives it a 5-star rating and he's not wrong to do so.
You might also want to look out for his work on the theology of the psalms, The Lord Reigns - another great resource.
