Ah, so you have found a few of the ten million out there on Youtube. Some of these people do great jobs with editing the videos - our future movie makers... here are some that I have found that are my favorites:
You will need to log in to see the video as they have disclaimer on there that some material may be inapproprite...blah, blah, blah. Youtube can be stupid at times, but I love the piano in the video and they throw in a few talking parts in sync with the music. Beautiful
In the book, "Brokeback Mountain: Story To Screenplay", Annie Proulx said that she listened to the song "Spiritual" as performed by Charlie Haden and Pat Metheny to write the scene where Jack has almost fallen asleep standing up and Ennis comes behind him and sings to him.
This music says what I feel in my heart when I think of this movie - sad, beautiful, peaceful, loving, longing, ok, I do not want to fill up the whole page!! My favorite!