The CD/DVD of Jacob Obrecht's St. Donation Mass has my head spinning about the magnificence of the timeless work of this genius.
Here is a piece of Obrecht's gorgeous work, an elaboration of the Salve Regina tune known to most Catholics in the middle ages before it was displaced by the more modern version that Catholics, if they have heard a Salve Regina at all (and most have not), know the best. So to understand this piece, imagine that the tune at the outset is deeply familiar - perhaps the most familiar Marian antiphon.