Here are some places where you can download some of the songs for the Twilight soundtrack:

Muse- Supermassive Black Hole
link

Paramore- Decode
link

Linkin Park- Leave out all the rest
link

Collective Soul- Tremble for my beloved
link

There's only a few, but they're free, and I don't know about everyone else but I really can't wait for the Twilight soundtrack to come out!
If you know any more places please add them below so other people can get them:)