I remember reading this sweet - and sad - story a long time ago but can't seem to find it again.  Sam got a brain injury when he was older and Dean looked after him, eventually bringing him to Bobby's house.  I think Sam had a little stuffed animal named Ted?  And at the very end the boys went to the Grand Canyon (I think) and Sam gave the stuffed animal to a little girl because he thought she needed it more than him.

This is driving me nuts, so if you guys can link me to the story that would be great.  Thanks!