I am a notoriously stingy rater [I've seen 4922 total movies, and given 532 films 8+], but these are my horror 8+ (according to IMDb tags):

[Rec] (2007) 28 Days Later... (2002) A Nightmare on Elm Street (1984) Alien (1979) Alien Raiders (2008) Alligator (1980) An American Werewolf in London (1981) Angel Heart (1987) Army of Darkness (1992) Baghead (2008) Behind the Mask: The Rise of Leslie Vernon (2006) Body Melt (1993) Braindead (1992) Cabin Fever (2002) Carrie (1976) Castle Freak (1995) Chained (2012) Children of the Corn III: Urban Harvest (1995) Cloverfield (2008) Cube (1997) Dagon (2001) Das Cabinet Des Dr. Caligari (1920) Dawn of the Dead (1978) Dawn of the Dead (2004) Day of the Dead (1985) Dead Silence (2007) Deadgirl (2008) Deliria (1987) Dèmoni (1985) Detention (2011) Død snø (2009) Død Snø 2 (2014) Dog Soldiers (2002) Dolls (1987) Dracula (1979) El espinazo del diablo (2001) Equinox (1970) Eraserhead (1977) Evil Dead II (1987) Final Destination (2000) Frankenstein (1931) Fright Night (1985) From Dusk Till Dawn (1996) Ginger Snaps (2000) Grave Encounters (2011) Hausu (1977) House of 1000 Corpses (2003) Idle Hands (1999) In the Mouth of Madness (1994) Invasion of the Body Snatchers (1978) Jeepers Creepers (2001) Killer Klowns from Outer Space (1988) Körkarlen (1921) Les Diaboliques (1955) Love Object (2003) Magic (1978) Martin (1977) May (2002) Mum & Dad (2008) Mumsy, Nanny, Sonny & Girly (1970) Pet Sematary (1989) Piranha 3D (2010) Popcorn (1991) Prince of Darkness (1987) Profondo rosso (1975) Psycho (1960) Race with the Devil (1975) Ravenous (1999) Rubber (2010) Saw (2004) Scarecrows (1988) Scream (1996) Screamers (1995) Sei donne per l'assassino (1964) Shaun of The Dead (2004) Silent Night, Deadly Night (1984) Stake Land (2010) Stalled (2013) Stir of Echoes (1999) Ta paidia tou Diavolou (1976) Tales from the Crypt: Demon Knight (1995) Taste of Fear (1961) Teeth (2007) Terror Train (1980) Tesis (1996) The Battery (2012) The Blair Witch Project (1999) The Blob (1988) The Burning (1981) The Cabin in the Woods (2012) The Cat and the Canary (1939) The Changeling (1980) The Collector (2009) The Devil's Rejects (2005) The Evil Dead (1981) The Exorcism of Emily Rose (2005) The Fly (1986) The Girl Next Door (2007) The Haunting (1963) The Hidden (1987) The Incredible Shrinking Man (1957) The Innkeepers (2011) The Langoliers (1995) The Last House on the Left (1972) The Lost Boys (1987) The Lost Skeleton of Cadavra (2001) The Loved Ones (2009) The Prowler (1981) The Return of the Living Dead (1985) The Serpent and the Rainbow (1988) The Shining (1980) The Signal (2007) The Texas Chainsaw Massacre (2003) The Thing (1982) They Live (1988) Thinner (1996) Tucker and Dale vs. Evil (2010) Waxwork (1988) Wishmaster (1997) You're Next (2011)