Just a quickie post to recommend a site and provide linky:
Horror Film History
From the 19th Century literary roots through to the 2000's, check out these essays on the dominant themes of horror throughout the decades. It's interesting reading, and it comes with "further reading" recommendations for those who like to jump all over the intertubz instead of, say, writing chapters of their stories that they're supposed to be working on... just as a 'for instance'.
I'm also thinking there should be some love for the Tabula-Rasa horror timeline, which is kind of fun to read through:
The Horror Timeline