Carrie (1976) Based on book that ended on Stephen King's trash bin. Thankfully, his wife recovered it. His first book!
The shower scene in Psycho was the scariest at the time. Watch it, if you dare: http://halloweentime.org/psycho-shower-scene
Horror Movie Posters: Could be tweaked to include party information .... smaller versions for invites and make a poster sized one/frame for them to keep! Could also use various old horror movie posters as decorations at the party.