I half agree with commenters that think The Road should not have any music at all, but that aside, I find this song very simple and beautiful:

Nick Cave & Warren Ellis "The Road (Main Theme)"
[via Gorilla vs. Bear]Mute has just released a new 2CD compilation, White Lunar, covering much of Ellis and Cave's best soundtrack work for films such as The Proposition and The Assassination of Jesse James by the Coward Robert Ford, as well as for The Road and lesser-known films.
Visit Other Music for more information and audio clips.

While we're at it: there are several clips from The Road on YouTube right now. I'm not sure why you would do this, but if you're like me and you have absolutely no self-control, have at it. [Be warned — I believe the MPAA term "unrelenting tension" applies.]

More on The Road here.