For today it has to be at least Hysteria. OOh... then Fury, Undisclosed Desires, Nishe, Citizen Erased, Stockholme Syndrome, Muscle Museum, Sing for Absolution, and Starlight. Time is Running Out is special to me (because that is was the first song my son learned when he was four). I can't fairly narrow it down to one today so I failed the question.
So let's just stick with Hysteria because I cannot believe the bass and energy in this one and it comes to mind first and currently has the most plays on my iPod.