Aradia, or, The Gospel of the Witches
"Aradia" may not need much introduction… but for what it's worth, it is the translation (a new translation is included, see below) of an Italian MS which was supposedly given to G Leland, purporting to detail practices of Italian witchcraft.
Various debates about the provenance of the material aside (debates which are detailed in both this book and in Triumph, already listed here), Aradia was clearly used as source material by folk such as Gardner and Valiente – it contains, for instance, the basis for what became the Charge of the Goddess.
The translation here is a new one, and much better than Leland's (the original is supplied, both in dialect and in Italian – reminiscient of some editions of Dante!).
For the notes and the translation, this is a very good edition of Aradia.