I watched a bunch of half hour scare-related animation. I won't talk about each, but I'll link to many of them so you can watch along.
It's the Great Pumpkin, Charlie Brown
I watched this last year and commented on it (as well as another TV special later in this list). You can find my comments here.
Pluto's Judgement Day
Lonesome Ghosts (my favorite Disney short ever. This poster hangs on my wall)
The Mad Doctor (also has an awesome Tom Whalen-designed poster)
Trick or Treat
Donald Duck and the Gorilla
Night on Bald Mountain
The Haunted House
The Legend of Sleepy Hollow
The embedding was disabled, but this is classic. As a kid, I only saw the edited for compilation version. Ichabod is kind of a dick in this and I kind of felt bad for Brom Bones. Amazing songs.
Garfield's Halloween Adventure (no link to full show)
Or, if you don't have time for everything, you should watch this because it rules and covers some of the same ground and a little more (all edited for time, though)