Here are a few books I use for my research as well as reference.
If you click the links, it will take you to Amazon.co.uk.
It’s a pretty esotheric list, with more added regularly, but these are the main ones I (currently) refer to.
The printed books, that is. I have a stack of ebooks at my disposal as well, a lot of them Grimoires of varying ages, books on Witchcraft, Demons, and of course, several on writing.
Some of the books are no longer in print!
Writers General Bookshelf
Fiction Writers Bookshelf
I own pretty much the entire series of the Howdunit Series published by Writer’s Digest, so I’ll just have a link to the series here. (Deadly Doses resides in my kitchen. Next to the cook books… You were warned.)
The Holy Bible – Sorry, no link for this. Mine is actually 150 years old.