Anca itibaren 36877 O Campo do Mouro, Pontevedra, Шпанија
Definitive reference for all aspects of early notation. There's a lot of very valuable information here. On the downside, the organization is not ideal--that and the fact that the index is barely sufficient) can make it hard to track down specific issues with certain notated types. Also, the facsimiles presented are very low quality.