This comes to you via The New Liturgical Movement. The St. Gregory Society, the "grand fortress of traditional Catholicism in Connecticut", has a CD available for sale; one of the free tracks is Tribus miraculis, a polyphony piece by the great Palestrina. It is absolutely beautiful... I've listened to it about five times this afternoon.
You can listen to it below. You can also see the music for this motet in a PDF (courtesy of the Choral Public Domain Library).
Here's the MP3 (3:48):
(Recycled from November 27, 2007)