Here's my list, no particular order:

• Dancers being cut in half in Ghost Ship

• Regan doing naughty things with a Crusifix

• Changing to a werewolf in American Werewolf in London

• Mowing down zombies with a lawn mower in Braindead

• The hooks from Hellraiser

• Michael Stabbing in the closet from Halloween

• The Shower Scene (of course, Psycho)

 I'm missing a TON I know...

Let's see...also in no particular order

• Jack Nicholson's "Heeere's Johnny" scene in The Shining

• the ax murderer busting the restaurant window in Mouth of Madness

• the little girl eating her mother's heart in the original Night of the Living Dead

• Dr. Weir (Sam Neil) explaining why eyes are unnecessary in Event Horizon

• Gary Oldman's Dracula licking the blood off of Jonathan Harker's straight razor in Coppola's Dracula   

• Peina (Christopher Walken) explaining to Kathy (Lili Taylor) that she is nothing in The Addiciton

• Constantine (Keanu Reeves) commanding the unseen entity to "come into the Light" in Constantine

• Hannibal Lector's escape in Silence of the Lamb 

No particular order...well kinda alphabetical order I guess...

• Lambert's death in Alien
• the cockroach swarm in Creepshow
• the entire 3rd act of Day of the Dead
• the firehose-style spray of blood out of the wall in Evil Dead II
• Ginny's run from Jason at the end of Friday the 13th Part 2
• Pennywise appearing through the hanging sheets at the start of IT
• Tina's death in Nightmare on Elm Street
• that horrible scene in the back bedroom from Pet Sematery...*shudder*
• the decapitation scene in Re-Animator
• the dinner scene in original TX Chainsaw

definitely more but im on my lunch break...gotta go ;)

Some of the unmentioned

• The Shining dog/butler scene
• The grudge head coming out of the closet
• The death of the mother in Carrie
• The death by garage door in Scream
• Tree rape Evil Dead
• The horse scene in The Cell
• Stabbing via ear of corn in some random Stephen King movie that was on TV
• "rUN rABBIT" NEED i SAY MORE?
• slow motion shoot out to freebird-devils rejects
• The pit of needles in Saw II
  

More of the unmentioned (i'm scanning my shelves as I go along here...):

-Johnny Depp and the bed (Nightmare on Elm Street)

-Kevin Bacon and the arrow (Friday the 13th)

-The "thing" in the bag (Audition)

-Christine's self-repair (Christine)

-Every aspect of the graveyard scene (Dead Alive/Braindead)

-Also, the entire third act of (Dead Alive/Braindead)

-The Chinese Restaurant scene (IT)

-The ending of (Night of the Living Dead)

One of the scenes that freaked me out, which is probably one of the reasons that I like Takashi Miike, is when Asami saws off Shigeharu's foot. I also liked the last 5 minutes of 1408.

I agree with alot of the ones already mentioned so here's a few I don't see mentioned.

woman dropping from bell in "Dracula Has Risen from The Grave"

"mother's" shadow on shower curtain in "Psycho"

Polanski crawling upstairs to throw himself out the window the second time in "The Tenet"

"Smoke Good" in "Bride of Frankenstein"

The scene with the dad saying he had poison ivy and the little girls saying they were itchy in "Slither"

The marines getting slaughtered in the dark in "Aliens"

The whole little girl in the bedroom scene in new "Dawn of the Dead"

The use of Johnny Cash's "When the Man Comes around"  and the clips they showed in new "Dawn of the Dead"

Sex scene in "Bram Stoker's Dracula"

Flyboy getting it in the elevator in original "Dawn of the Dead"

The ending of "Sixth Sense"

Brad Pitt discovering his wife's head in "Se7en"

Susan Sarandon's breasts in "Rocky Horror Picture Show"  when she says "Touch Me-- I want to feel dirty"

The drunken singing and swapping of scar stories in the Orca in 'Jaws"

The ending of "Jeepers Creepers"

Heather Graham in "From Hell"

Michael Myers missing when Loomis looks down in original "Halloween

The sledgehammer and meathook kills in original "Texas Chainsaw Massacre"

"They're Coming to get you Barbara" in "Night of The Living Dead"

Folded girl in dresser drawer in "Mother's Day"

Transformation in "Altered States"

Sarah stabbing and leaving Juno in "The Descent"

vampire boy outside window in "Salem's Lot"

Sex scene in "Cemetery Man"

death by sunlight scene and the ending  in "Interview with the Vampire"

The ending of "High Tension"

The first kill in "Perfume"

The creature in "Relic" pulling the cops off their ropes

The ending of the "Howling"

First kill and handcuff scene in "Innocent Blood"

"I've got a growth on my Pecker" in "Bubba Ho-Tep"

Mermaid man in "House of 1000 Corpses"

Zombies coming out of water in "Land of the Dead"

there's just too many

The ending of - Inside

Zombie/shark fight scene - Zombie

Head spin - The Exorcist

Lamebrains outburst rant not sure exactly what was spoken - Night of the Living Dead (1990)

Music playing (Queen) / beating bartender - Shaun of the Dead

Blood testing scene - The Thing (remake)

Hand crawling - The Hand (homemade movie done on super 8)