The haunting choral piece from the beginning of the final trailer is very likely from "Two Steps From Hell", which is a company (like X-Ray Dogs) that specializes in music for film trailers. It is not available for sale.
You can read about their policy regarding the sale of their music here.
You can see a list of their credits, including Twilight, here:
I am desperate. I need to have the trailer music to Twilight. Does anyone know what it is? Not Red Mist and Not Angels.. Its something else.. I am at a loss. It is killing me. I have searched till my eyes are blood shot. Save me!!
WhiskyGirl07, I think I know what you mean... I'm looking for the choral piece, not just the individual vocals in the beginning, which are from the "Two Steps From Hell" and that starts from :10 seconds in until 0:36= choral piece?, probably done by Xray dog through 1:00-ish
From my research, the song IS by Two Steps From Hell and is titled "Mercy In Darkness". You can find a video on YouTube, but that may be all. I don't think there is a download available, as others have previously mentioned. That's unfortunate, but at least we're finally able to identify the music! I love it!