I just wrote a new research paper called "In Praise of Mainstream Music: an index of familiar songs from sources outside our philosophy".
Built from the input of many music directors and music helpers, this paper discusses the pros and cons around using music in our NT services that doesn't come from NT composers - music from pop sources like Marvin Gaye's "What's Goin' On", traditional church sources like "His Eye is on the Sparrow", music theatre sources like "Seasons of Love" from Rent, or contemporary mainline Christian rep like "Open the Eyes of My Heart".
Check it out as the newest article on my resources page, which hosts free material to help New Thought music ministries.