There was this fic I found several months ago (and lost because of the delicious thing.) It was a long one, a wincest, where Sam's dying and Dean takes care of him as he degenerates. 

Sam starts hearing birds and makes Dean take him to a doctor, who says he has… something, I think it was brain cancer. They stay at an apartment and it switches points of view alot to amp the angst. There's this one really great scene where a Jehovah's Witness knocks on the door and Sam chews him out about the realities of heaven, angels and dying. Sam dies at the end. 

I'm fairly certain the fic was part of a calendar project, a J2/Sam-Dean thing where she did one a month based on her favorite fics.