Poey-d'Avant, F. Monnaies Féodales de France. (1858).
Still one of the finest works on French feudal coinage available, and available online. Includes dozens of plates in the three volumes, although the scanning resolution is such that the details are difficult to make out.
PDF downloads available online at Google Books:
Vol. 1: 1 - 2337
Vol. 2: 2338 - 4664
Vol. 3: 4665 - 7003
See French| coins| for sale| in the Forum| Ancient| Coins| shop|.