If I went back to buying horror books I would have no money left.
the last i bought was the Amicus book(the studio that dripped blood? House poster is on cover).
I started collecting when I was a wee lad..the ones I remember off hand are Classics of the Horror Film and Pictorial History of the Horror Film(both have lots of great pics of pre 1975 movies).
The latter has lots of Hammer stuff-movies (like the Reptile) that i didnt see until decades later.
More Classics of the Horror Film isnt so good-covers 74-85 movies).
The Vampire Cinema by David Pirie-lots of good pics and some interesting anecdotes.
Another favorite is a book on Aurora Model Kits by Thomas Graham(I think), it even includes fan created box art for never released kits on the Invisible Man etc.
Another excellent one is the 1986 Penguin Encyclopedia of Horror and the Supernatural, covering a wide range of horror in culture.
I really want to get the Hammer Story by Alan Barnes and Marcus Hearn
and one of the newer Harryhausen books(since the Film Fantasy Scrapbook goes back to 81) but I keep forgetting.