I don't bother with Halloween, as I spend a lot of time thinking about dark and weird stuff, so it's a holiday for me. I do like horror movies, but most modern ones try far too hard, and are just not frightening at all. Not a lot of thought put into the writing of most, either. I'll stick to some of the old ones, thanks.
01) Night Of The Demon (1957)
02) Haxan (1922)
03) The Cabinet Of Doctor Caligari (1919)
04) The Living Dead At The Manchester Morgue (1974)
05) Brides Of Dracula (1960)
06) Death Line (1972)
07) From Beyond The Grave (1974)
08) Blood On Satan's Claw (1971)
09) Re-Animator (1985)
10) Tombs Of The Blind Dead (1972)
I've spent an awful lot of time trying to watch as many horror movies as I can, so to pick ten is really difficult. A good horror movie should stay in your mind for an uncomfortably long time after you've watched it. All of the above do just that.
Saying that, any of the 1960's and 70's Hammer, Amicus, Tigon, and AIP movies are a good way to spend an evening. The 1930's and 40's Universal horrors are now more charming than terrifying - except for maybe 1934's 'The Black Cat', which is still very dark in tone, with hints of necrophilia.
Old horror movies; I love 'em all.
I do find 'The Exorcist' completely unfrightening, though. It's overwrought nature makes it very funny to me. And that was long before 'The Naked Gun' used it as a visual gag.