At the opposite end of the spectrum of liturgical music from the fine work of Carlo Rossini are the two "Gradualia" of William Byrd, published in 1605 and 1607.
Byrd was one of the greatest English polyphonic composers, born about 1540. He is probably best known for his three Mass setting (for 3, 4 and 5 voices) and his "Great Service": settings (in English) of the major texts for Anglican Matins and Evensong.
His Gradualia provide elaborate polyphonic settings of Mass Propers, in particular a full set for all the Masses of Our Lady.
I have heard these Byrd setting used once liturgically, in the chapel of University College Durham. The choir also sang a Byrd setting of the Ordinary of the Mass and the result was, frankly, a bit too much. It was rather like eating a meal at which there was chocolate in every course.
I am keen to use the Byrd Propers however and think that this could be done by combining them with a Chant Ordinary. This would be something of a reversal of the normal contrasting music for Mass - Chant Proper and polyphonic Ordinary - and would be an interesting experiment. I have already discussed it with one of my polyphonic collaborators as a possible project for 2007.
For anyone wanting to hear these Byrd settings of the Proper, The Cardinall's Musick directed by Andrew Carwood have undertaken a large project recording Byrd's music and extracts from the Gradualia can be found on those recordings. I am listening to their CD "Laudibus in sanctis" (which includes the full Proper for Marian Masses of Paschal Time) as I write this.