I think this movie would probably be the perfect example of what I'm looking for: a movie that takes place during Autumn and looks/feels like it. A lot of movies try to do this but never really succeed.
The Village and The Sixth Sense both take place entirely in autumn. I don't know that I could sit through The Village again if you paid me though.
The Others is a good one.
Though more comedy than horror, one of my personal favorites to watch in October, which actually takes place on Halloween, is Arsenic and Old Lace. Most of the film takes place in the house but trick or treaters do show up at the door and the cemetery scene screams autumn.
The Stephen King story Riding The Bullet has a huge Autumn feel to it and also takes place on Halloween. Gets a lot of bad reviews but I still thoroughly enjoy it.
I don't think anyone mentioned the FIRST Halloween! Nuts. I also agree with the above poster who said to watch the opening of Halloween 4, the title sequence nails it.
Evil Dead 2 is great, forest full of dead leaves, demons, blood, violence--you got it all.
Fallen with Denzel Washington has some beautiful autumn scenery in it, and its about demons. I think its a great movie if not marred a bit by some poor narrative choices towards the end.
Night of the Living Dead (the original) is perfect for this time of year.
Return of the Living Dead, I think, takes place in the summer, but I'll tell you, it has the autumn imagery in my opinion. Check it out. Zombies crawling out of graves and all of it. I think Thriller must have been inspired by it (or it by Thriller, I can't remember which came first).
Hell, watch the full Thriller video for what it's worth, that's a great 13 minutes.
Practical Magic Hocus Pocus The Lady in White Halloween 1-7 Goosebumps (the film) Trick or Treat Night of the Demons Beetlejuice Casper Corpse Bride The Little Vampire
Not all horror films.
You keep on reminding me of a darkness only I can see
All Hallows' Eve 1 & 2. Although 'All Hallows' Eve 2' to me felt more Halloweeny and has more orange / Autumn visuals and less darker than the first film, these two films are not too bad actually, there's a great little story about pumpkin carving in the second film that I really liked.
'Idle Hands' a great very under-rated Halloween horror comedy. Such a fun movie!
'The Barn'... There's a new movie supposably out this year but I haven't got to see it but REALLY want to, I'm not sure if it actually got released in time for this Halloween but it looks like something I might love as it has a throwback 80s look and feel to it from what I seen in the trailer, so from the trailer alone I'm hoping it's going to be good and worth recommending here to keep a look out for.