Halloween Bingo Preparty Supernatural Series
In general, it would have to LOTR. Because I've read one copy into the ground.
But this year, my top three Halloween fitting titles would be:
The Women of the Otherworld series. - I believe this was Armstrong's first series. At times it shows, but you can see her developing as a writer (and she works with her editor). What I really love about this series is not only does feature women, but each woman is strong in her own way. And I say this as someone who didn't like all the women in the series. Additionally, the women are friends with each other.
Merrily Watkins - I've developed a love for series, mostly because of the characters and the use of English folklore.
Count St. Germain Series (counting the Olivia books) - world's greatest vampire.