I have always had an idea of a female hunter alongside Dean and Sam.
Kasey Daley Mueller:
Played by Gemma Arterton
Auburn medium lenghthed wavy hair
Brown eyes
Pale skin
British accent
A witch ( And not just any other witch; a special community of witches whose virgin blood is on Heaven's and Hell's most wanted)

She is two years you ger to Dean and is a shy but a kickass hunter. She has a romantic tension with Dean till 2x1 in my time of dying.....where John and Kasey make up a plan to make it look like Kasey was the one who forced him to sacrifice his life to save Dean's. (So that the brothers think she took revenge for the fact that John had to kill her father years ago on a hunt without a choice. ) but truth is that she never had vengeance it was a clever articulated by John her to deliberately make Dean hate her forever because they know about an ALL Powerful Destiny that in the near future Kasey has to sacrifice her life for the greater good and they all know that if the romantic connection continued, Dean would never allow anythibg like that to happen

So till the whole of second season, Dean can't stand her sight. He tells her never to show her face again to him.....she is heart-broken but is helpless. They start warming up a little in season 3 and she without his knkwledge teams up with Sam to try her best to save dean from going to hell. But in vain

In season 4, 4x18, they come to chuck shurley. There, they find books each of which has carefully been manipulated to erase any sign of Kasey. In short its like there was noone called Kasey in their whole lives....Sam and Dean dont find that so disturbing as Kasey. She thinks this has got to do something with her destiny and gets worried. She calls Castiel about this and he replies "the prophet's word cannot be false." They come to a shocking possibility that in near future Kasey might be COMPLETELY erased from the brothers memories. This is the same episode where Sam reads the books.In the part where John dies, it is revealed Kasey was infact simoly complying to Johns plan of making her look like the culprit. Dean is heart broken to have treated her like that and tries to ask her why she did that but she doesnt reply.....

I have extended it and have a lot of stories......if ypu guys like it i would love to share!!:)