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
Random House Webster’s Word Menu
Read the review here
First Draft in 30 Days – Karen Wiesner
The Synonym Finder (Hardcover) – J. I. Rodale
Fiction Writers Bookshelf
I own pretty much the entire series of the Howdunit Series
The Holy Bible - Sorry, no link for this. 
Mine is actually 150 years old.
The Writer’s Guide to Places – Don Prues and Jack Heffron
Who’s Who in Non-Classical Mythology – Egerton Sykes
A Dictionary of Angels: Including the Fallen Angels – Gustav Davidson
Vampire: the Encyclopedia – Matthew Bunson
Vampires, Burial and Death: Folklore and Reality – P Barber
The Vampire Book: Encyclopedia of the Undead – Gordon J Melton / Martin V Riccardo
To Ride a Silver Broomstick: New Generation Witchcraft – Silver Ravenwolf
