DnDChick
Demon Queen of Templates
Here is a list of books, stories, and movies that are not Mythos-related, but which have the appropriate atmosphere. Some are books or stories, some are movies, some are both. (Lotsa Stephen King...)
Species 1 and 2 (for the 'aliens among us' plot)
Children of the Corn (secluded town, mad cult, big monster in hiding)
It (hidden alien evil devouring children, combatted by everyday people)
Mimic (monstrous insects in the sewers)
They Live (another one for the 'aliens among us' line)
Graveyard Shift (for the big nasty mutated rat)
Tommyknockers (hidden alien evil mutating people and making them work to free them from imprisonment)
Moontrap (aliens on the moon making nasty cyborgs)
The Blair Witch Project (for the mysterious, sanity-shaking evil hidden in a deep, dark forest, and the investigation leading up to the climax in which everyone dies lol)
The Curse (this is basically a modern retelling of the Colour Out of Space, and gets pretty nasty in places, especially since it stars a pre-ST:TNG Wil Wheaton lol)
Lair of the White Worm (vampire snakes, cults, big nasty wormy creature in a cave)
Nightwing (communal killer vampire bats led by a ghostly shaman)
The Manitou (woman impregnated with a monstrous Native American spirit...this is a pretty bad movie, but it stars Tony Curtis so it cant be all bad!)
Altered States (a man experiments with sensory deprivation and goes too far over the brink of sanity)
Any others you would like to share?
Species 1 and 2 (for the 'aliens among us' plot)
Children of the Corn (secluded town, mad cult, big monster in hiding)
It (hidden alien evil devouring children, combatted by everyday people)
Mimic (monstrous insects in the sewers)
They Live (another one for the 'aliens among us' line)
Graveyard Shift (for the big nasty mutated rat)
Tommyknockers (hidden alien evil mutating people and making them work to free them from imprisonment)
Moontrap (aliens on the moon making nasty cyborgs)
The Blair Witch Project (for the mysterious, sanity-shaking evil hidden in a deep, dark forest, and the investigation leading up to the climax in which everyone dies lol)
The Curse (this is basically a modern retelling of the Colour Out of Space, and gets pretty nasty in places, especially since it stars a pre-ST:TNG Wil Wheaton lol)
Lair of the White Worm (vampire snakes, cults, big nasty wormy creature in a cave)
Nightwing (communal killer vampire bats led by a ghostly shaman)
The Manitou (woman impregnated with a monstrous Native American spirit...this is a pretty bad movie, but it stars Tony Curtis so it cant be all bad!)
Altered States (a man experiments with sensory deprivation and goes too far over the brink of sanity)
Any others you would like to share?