Oh, okay then (leaving out tv movies like SALEM'S LOT, THE STONE TAPE, DON'T BE AFRAID OF THE DARK, THE WOMAN IN BLACK, etc.)
THE INNOCENTS
THE HAUNTING
VIDEODROME
TARGETS
SUSPIRIA
DEAD RINGERS
THE FLY
THE THING
DAWN OF THE DEAD (orginal)
NIGHT OF THE LVING DEAD (original)
THE EXORCIST
DON'T LOOK NOW
PHANTASM
INVASION OF THE BODY SNATCHERS (original and '78))
BLACK SABBATH
BLACK SUNDAY
HALLOWEEN (original)
TEXAS CHAINSAW MASSACRE (original)
PSYCHO
ROSEMARY'S BABY
BLACK CHRISTMAS (original)
NOSFERATU (original)
JAWS
THE SHINING
SILENCE OF THE LAMBS
EVIL DEAD
ALIEN
NEAR DARK
REANIMATOR
LET'S SCARE JESSICA TO DEATH
CAT PEOPLE (original)
THE DESCENT
THE RING
AN AMERICAN WEREWOLF IN LONDON
CREEPSHOW
KWAIDAN
ONIBABA
SESSION 9
DAGON
(and probably about 10 others I've forgotten)
With some minor exceptions, I imagine these are all equal to each other - not equally as GOOD, but they encompass a pretty wide range of what horror is capable of. I wouldn't personally count ALIENS, as it's a war movie where the enemy are aliens (ALIEN, on the other hand, is pure monster movie) . But then, action-horror in general is not my bag (if you can defeat the threat just because you get your hands on a bigger gun, well, that ain't horror to me. Might be horrifying, but...)
I left off some personal faves (THE FOG, THE BLIND DEAD, CABINET OF DR. CALIGARI, THE FALL OF THE HOUSE OF USHER - Corman version, CARNIVAL OF SOULS - original), a spate of monster movies (like CREATURE FROM THE BLACK LAGOON, THE TINGLER), and the Universals (FRANKENSTEIN def.), Val Lewtons (THE BODY SNATCHER - Karloff's best ever role!) and Hammers (CURSE OF THE WEREWOLF) because they wouldn't have a chance anyway.
Also didn't include quasi-horror like THE WICKER MAN or THE SEVENTH VICTIM, or horror comedies (like RETURN OF THE LIVING DEAD, DEAD-ALIVE or THE ABOMINBABLE DR. PHIBES) or recent faves (SAUNA, FEARS OF THE DARK, LET THE RIGHT ONE IN - thanks for the remind, Deflective!).
I'm kind of the opposite of Ms. Mac - I trend backwards and find most modern horror films unsatisfying (which is not to say that there haven't been some good ones recently) and the older stuff to have more meat, atmosphere, depth, creativity and honest emotion. Modern horror films are suffering a dilemma both long term (cultural trending from superstition to science), economic (movies cost more, and formulas assure money, so formula is what you get) and, most obviously, creative. The fact that director's/screenwriters frequently fail the audience (rote plot, uninvolving characters, standard scares) is matched by an audience that almost as frequently fails good movies (the death of "willing suspension of disbelief" as a fruitful stance, as that gives up too much control to the filmmakers, and hyper-criticality of audiences that demand "authenticity" but easily accept pandering).
My prediction as per a poll is that the monster movies and psychological horrors fall off first, then the subtle ghost movies and slasher movies, leaving in the end the masterfully WTF pieces, whatever their subgenre, and the childhood faves. If pressed, I know what the top 5 would be for me, but they encompass the five corners of horror and each would likely be unsatisfying to someone - horror is just too darn big top have a greatest!
PS - if this is considered last minute dumping, please just ignore the whole thing.