I'm not sure if I would call them cult related. The plot does involve a book of the dead and there is supernatural possession, but they are not dark movies.
I had forgotten that Sam Raimi was the director and writer or cowriter of all three.
Here are the premises for each:
The Evil Dead (1981):
Five friends go up to a cabin in the woods where they find unspeakable evil lurking in the forest. They find the Necronomicon and the taped translation of the text. Once the tape is played, the evil is released. One by one, the teens become deadly zombies. With only one remaining, it is up to him to survive the night and battle the evil dead.
Evil Dead II (1987):
A sequel/remake of the film The Evil Dead. A young man named Ash takes his girlfriend Linda to a secluded cabin, and plays back a professor's tape recorded recitation of passages from the Book of the Dead. The spell calls up an evil force from the woods which turns Linda into a monstrous Deadite, and threatens to do the same to Ash. When the professor's daughter and her entourage show up at the cabin, the night turns into a non-stop, grotesquely comic battle with chainsaw and shotgun on one side, demon horde and flying eyeball on the other.
Army of Darkness (1992):
In this sequel to the Evil Dead films, a discount-store employee ("Name's Ash. Housewares.") is time-warped to a medieval castle beset by monstrous forces. Initially mistaken for an enemy, he is soon revealed as the prophecised savior who can quest for the Necronomicon, a book which can dispel the evil. Unfortunately, he screws up the magic words while collecting the tome, and releases an army of skeletons, led by his own Deadite counterpart. What follows is a thrilling, yet tongue-in-cheek battle between Ash's 20th Century tactics and the minions of darkness.