Big Bang is awesome! I just read one of the best Sam/Dean fics ever. After a long time, here is a story that captures the boys voice perfectly. It weaves the main events of the series with the au seamlessly and makes me think , that 'the more things change the more they remain the same', when it comes to these two.
It's Courting Death by theproblematique:
SUMMARY
Sam Winchester lived the first six months of his life in a happy family; the next twelve years as John Winchester's only son, and the last decade as an orphan. He's supposed to die at twenty-two trying to save the woman he loves from a fire, because he doesn't have a brother to pull him back. But the night Sam meets his Reaper he discovers that Death is overly fond of pop-culture references, too beautiful to be real, and reluctant to kill him.
Link:
http://archiveofourown.org/works/875482/chapters/1682682