1979's "PHANTASM" ...in addition to surrealism, sudden shocks, and one extremely groundbreaking scene of graphic violence, this movie was also intensely strong on atmosphere. As a horror movie, I think of it as a nine-course meal, with a different kind of spooky fun every moment.

"Children Shouldn't Play With Dead Things" (1972) is also really strong on brooding, dreadful atmosphere!

i'm all over phantasm ..

a lot of the japanese horrors are effective because of their stylish atmosphere ..

ju-on (or the Grudge american remake) are great examples.

Never saw it...I heard it was good though (both versions).....

For me The Shining (original) has great atmosphere. I also really liked The Devil's Rejects because when I walked out of the theatre after watching it I felt almost dirty.

I also love the original Dracula for atmosphere, it was all about atmosphere back then. I think Night of the Living Dead (original) was a good one for this too....actually, I find a lot of the original black and whites had more atmosphere, they had to rely on it more than shock and gore.

Not so horror, but had lots of atmosphere for me was Requiem for a Dream...and Pi...but I love darren aronofsky so it could just be me.

Alot of great ones have been mentioned, but heres one that hasnt: Session 9. Amazing atmosphere, creepy and claustrophobic. I love how, like the original TCM, it didnt resort to setting everything in dark rooms or at night to create the atmosphere. Though some of it's best scenes were in the dark, it still held the atmosphere through the daylight hours. One of my favourites, very atmospheric.

yep, thats a great example

Not really horror, but, Batman Begins has some of the most amazing cityscape atmosphere i've ever seen.

The Changeling

It's the lighting.

They had to light the sets differently with black and white than they do now with color, creating that spooky, bizzare "glowing" type of atmosphere we love to see in classics like Dracula ('31) and The Haunting ('63).

Another great atmospheric movie, actually, one of the best, now that I think about it, is:

Freaks (1932)

This has amazingly dark and bizzare set pieces, and such an uncomfortable atmosphere and mood throughout. If anyone hasn't seen this, I highly reccomend it. (This was directed by Tod Browning, who also directed Dracula ('31))

Also, The Cabinet of Dr. Caligari (1920) relied almost 100% on atmosphere, and it worked. With a brilliant set and very limited lighting, this film still works today.