The twin girls seen in the vision from the Alpha Vampire is a reference to the twins seen in this movie, which in turn references the photograph "Identical Twins, Roselle, New Jersey, 1967" by Diane Arbus.
The name for a Twilight megafan - "Twihard" - is referenced in the episode's title. Dean also refers to himself as being Pattinson AKA Edward Cullen in the movie series Twilight