In the past, I've simply linked to my scary movies category, and possibly supernatural & paranormal movies. But then it occurred to me that there may be movies worth watching on Halloween in other categories, so... you should still definitely check out those first two categories, if you're looking for ideas for what to watch on or around Halloween. (Also check B-movies and giant monsters.) But here are a few other suggestions (though it's entirely probable you could find other movies scattered throughout my various categories that you would consider appropriate for Halloween, but which I don't include here). Note: in 2017, I redesigned my scary movies section into subgenres, some of which now include movies I used to list here, but which I've now deleted from this page, as it seems redundant to keep them here. And in 2019, I started a Halloween movies page in my movie reviews section, so I'll once again delete some things from this page.
I also think there are some TV series that are particularly apt around Halloween. Most of them can be found in the horror shows category. But there may be a few other things worth checking out in other categories, so I'll list them here, as well. Oh, and some web series.
The Black Cauldron
The Book of Life
Cowboy Bebop: The Movie
Graveyard Jamboree (short)
Hotel Transylvania, Hotel Transylvania 2
Mysterious Mose (short)
The Nightmare Before Christmas (mainly a Christmas movie, but it works for Halloween, too)
Scooby-Doo and the Witch's Ghost
animated TV series
The Grim Adventures of Billy & Mandy
Scooby-Doo, Where Are You!
live-action TV series
Garth Marenghi's Darkplace
Over the Garden Wall (animated)
see supernatural & horror webseries