Josh responds: "I'll try, Dan, but I can't promise much. I don't like vocal music, so I don't own much - off the top of my head, I think all I've got is: the Missa Solemnis, a Vespers and a Mass by Rachmaninov, Mahler's fourth and eighth symphonies, Beethoven's ninth, Anonymous 4 doing Hildegard von Bingen's chants for the Feast of 11000 Virgins, Debussy's "Pelleas et Mellisande", and some Brahms settings of love songs from some era or another."

The Missa Solmnis isn't a bad place to start as far as choral works are concerned. There's a ton of very cool a capella stuff out there, though. I strongly recommend looking into Frank Martin's "Mass for Double Choir". In fact, just let me know and I'll make a copy of it available to you.