One of the most famous Spanish flicks, but I guess it hasn't got the world-wide recognition other local movies have had (Almodovar's films, Oscar candidates, etc.).
El Día de la Bestia comes in the traditional B-series horror movie tradition, with Spanish caspa thrown in for laughs. It's basically about a priest (Álex Angulo, a splendid Spanish actor) who finds out that Satan itself's gonna be incarnated on Christmas Day.
Of course, he's got to go underground for further info, so he naturally checks the heavy metal scene, where he finds an unclassifiable jerk (played by 'showman' Santiago Segura, who is also an unclassifiable jerk) that sets out to help him. They join forces with a reality-show presenter/medium on their mission from God.
El Día de la Bestia is directed by Álex de la Iglesia, better known for Perdita Durango, a really curious individual.