Am I Not Human? - Two Steps From Hell from Invincible
While it sounds “Tron-ish”, it was never actually used on the movie or the trailers, for that matter, but for a Coca-Cola advert related to “Tron: Legacy”. (The one which said something about an App you could download to play Light-cycles with your friends, using your smartphone)
Anyway, I wished they could have used this one, at least for a teaser trailer.