kate+sam.
She's a psychic. We went to her when we needed to figure out who'd raised Dean from hell. Which was Cas, of course, and she tried to see his true form, and - that's what happens when humans see angels.
And then the next time we saw her, we got her killed by a demon, but since she's not injured I don't think she's lived that part yet. Last I saw her she was in heaven.