Recommended Commentaries
Summer in the Psalms (Summer of 2015 will cover Psalms 1-11)

Allen Ross - A Commentary on the Psalms: 1-41 
Gerald Wilson - Psalms Volume 1 (NIV Application Commentary)
James Montgomery Boice - Psalms Volume 1 (An Exposotional Commentary)
And of course, you have to check out the Prince of Preachers: 
Charles Spurgeon - The Treasury of David or online version