Machaut and the French Ars Nova by Hope Greenberg Graduate student paper. Today his four-voice Mass of Notre Dame is a textbook example for medieval counterpoint, and has served sufficiently to maintain his reputation across shifts in fashion.
Site is completely in French, but there are some audio files to which to listen.
A short biography and small picture gallery. This is both a reasonably complete discography of Guillaume de Machaut written in 1998 as well as a compendium of Machaut's musical lyrics gathered in 1999.