It all depends too. Are you looking for american horror movies? or it doesn't matter?
I'm a HUGE J and K (Japanese and korean) horror buff. Personally asians horror is the BEST horror movies. Well REALLY I love non-american horror movies.
Number one favorite is dumplings! It's Chinese horror, it's horror on another level.
Heres my list! (I own all of these)
Ju-On (the original grudge)
RIngu (the original ring)
Thirst (greatest vampire movie ever)
One Missed Call (original, not american remake)
A Tale of Two Sisters (also remade in America)
Premonition (not the Bullock movie)
The Eye (the original one)
Imprint (Miike's episode of Masters of Horror)
Carved: The Slit Mouthed Woman
The Red Shoes
Tokoyo Gore Police
Save the Green Planet!
Higurashi no Naku Koro ni Live Action (aka When The Cicadas Cry)
Ichi The Killer (2001)
DON'T EVER WATCH AN AMERICAN REMAKE OF ANY FOREIGN HORROR MOVIE! THEY ALWAYS FIND AWAY OF MESSING THINGS UP!
You can also find good movies by directors.
George A Romaro
Guillermo del Toro
and many more!