I haven't seen a lot of horror, including a number of the big titles (egs. Rosemary's Baby, Texas Chainsaw, Dr. Caligari), but ok, sure, I'll play!
1. Alien
2. Peeping Tom
3. Shaun of the Dead
4. Jaws
5. Psycho
6. Frankenstein
7. Young Frankenstein
8. Arsenic and Old Lace
9. The Thing (1982)
10. The Birds
11. King Kong (1933)
12. Night of the Living Dead (1968)
13. Tremors
14. Night of the Hunter
15. The Fly (1986)
16. The Phantom Carriage
17. The Shining
18. Aliens
19. Un chien andalou
20. M
21. Dark Water (Honogurai mizu no soko kara) (2002)
22. The Act of Killing
23. Invasion of the Body Snatchers (1956)
24. And Then There Were None (1945)
25. Frenzy
26. Bride of Frankenstein
27. Invasion of the Body Snatchers (1978)
28. The Invisible Man (1933)
29. An American Werewolf in London
30. Carrie
31. Wait Until Dark
32. The Exorcist
33. Nightmare on Elm Street
34. Tucker and Dale vs Evil
35. The Changeling
36. Drag Me to Hell
37. 28 Days Later
38. The Most Dangerous Game (1932)
39. The Evil Dead
40. American Psycho
41. The Descent
42. The Host
43. Let the Right One In
44. Halloween
45. Pan’s Labyrinth
46. Triangle
47. Blair Witch Project
48. Arachnophobia
49. Zombieland
50. Frozen
51. Sunshine
52. Coraline
53. Hard Candy
54. Misery
55. Cloverfield