''Do you realise that if cas didn't send Dean back in time to intervene with John's car buying in In The Beginning, Sam and Dean would be riding around killing demons in a Volkswagen van...'' Hahahahaha!! Awesome!! / Supernatural + Scooby Doo :)
Let's not forget A Very Supernatural Christmas, Jump the Shark, and Mannequin 3: The Reckoning. There are so many episode titles that are a play on words for real movies and TV shows. Yet one more reason I love this show.