Mine would be:
(1) The Haunting (the original) -- best horror film ever made. Absolutely terrifying with the loud booms and the expanding closed door.
(2) The Innocents -- who can forget the moment with the tear on the slate in the classroom? or Miss Jessel glowering in the rushes in the pouring rain?
(3) The Devil's Backbone -- A great setting (a boy's orphanage under siege in the middle of a wasteland during the Spanish Civil War), a scary pool, and a great creepy ghost. Plus, Eduardo Noriega as his studliest.
(4) The Woman in Black -- A great haunted house in a great setting, and a great scary ghost. The sequence where the ghost emerges from a door at the end of a hallway behind Daniel Radcliffe is very scary
(5) The Shining -- The whole film isn;t as scary as the early parts, but the sense of disorientation and menace in the beginning is great, as are the famous Steadicam shots from danny's point of view on his Big Wheel
(6) The Others -- Another genuinely great haunted house, with first rate performers (Nicole Kidman in her best performance to date, Fionnula Flannagan, Christopher Eccleston, and that great child actress). Beautiful sense of atmosphere, and a fine emphasis on character
(7) Session 9 -- The whole doesn't quite come together, but this has the best pre-existing setting for a horror film ever: the crumbling and abandoned Danvers State Home for the Insane (since demolished), which may or may not be the home to either ghosts or to former inmates who have come back to threaten a hazmat team
(8) The Invasion of the Body Snatchers (either version--they are equally good) -- These are usually grouped with sci-fi films, but they are truly horror films, and they both have excellent claustrophobic paranoid atmospheres, and each offers a great hysterical performance--Carolyn Jones in the original and Veronica Cartwright in the remake
(9) The Birds -- Again, although rarely admitted to be a straight horror film, it really is one. The confused family tensions have something to do with the random attacks of the birds, but what, exactly?
(10) Inferno -- The whole movie is not good at all, but the beginning sequence--where the heroine drops her keys into a submerged room beneath her feet, and must dive in for them--is both beautiful and terrifying.