Writing Prompts:
Wrentham Public Schools: Halloween Writing Activities and Ideas
Pinterest Boards:
Halloween Classroom Ideas
Halloween - School Ideas
General:
The Teacher's Corner (crosswords, word search, etc.)
Education.com (a lot of classroom activities here)
Scholastic (includes Math and Science activities)
Cybraryman's website (pretty much everything you can think of here)
LiveBinders:
By Wisermar: