Directory for the Public Worship of God - http://www.reformed.org/documents/wcf_standards/index.html?mainframe=/documents/wcf_standards/p369-direct_pub_worship.html
Trinity Hymnal (Revised) - http://www.opc.org/hymnal.html
Scriptural Regulative Principle of Worship (Williamson) - http://www.westminsterconfession.org/worship/the-scriptural-regulative-principle-of-worship.php