Nearly a year and a half ago, I came across a must have book for every choir director’s shelf, Choral Repertoire by Dennis Shrock. Mr. Shrock presents the major repertoire spanning the history of Western choral music, from Medieval to Modern, with notes on more than 5,000 works, arranged in such a way to make research easy. Since a vast portion of that music is sacred in character (and much of that specifically written for use in the Catholic Church), the book is invaluable for the church musician. I find the section on Modern Music helpful in finding new works for use in the liturgy, from settings of the Mass to motets. You can buy it here on Amazon.