The ending of Fobia: St. Dinfna Hotel. You spend the whole game investigating a haunted hotel used by the occult, fighting zombies and assorted monsters all the way, only to realize in the last stage that the hotel is actually a front for a high-tech facility meant to research the underworld.
Web Original
The 1491s have "Cabin in the... Forestses", though the only similarity beyond the shout-out name is that the horror-comedy sketch takes place at an isolated log cabin.
The Red vs. Blue PSAs "New Holidays" has a list of new festivities, one of which is simply "Kevin" ala the betting board.
SCP Foundation: SCP-2786 is a metaphysical entity that can insert itself into horror narratives, where it attempts to portray itself as a brave hero and alter the story itself. One of these happens to be Cabin in the Woods.
Western Animation
Robot Chicken: In Immortal, it is said that the show itself is made to appease the gods. One character points out that this is exactly like Cabin in the Woods.
", though the only similarity beyond the shout-out name is that the horror-comedy sketch takes place at an isolated log cabin.