The second movement from Beethoven's 7th.
http://www.youtube.com/watch?v=4uOxOgm5jQ4
Staggeringly sad/beautiful piece of music and a cool video too.
people frequently consider this the greatest piece of classical music ever composed. I don't know if I'd go that far, but it is certainly top five. the methodical, plodding nature of the opening notes, you seriously are almost destroyed by the heart wrenching agony behind the melody. It almost literally sweeps you up with its power, growing and growing into an almost rhythmic heart beat, decimating your audio senses. The second half is like a affirmation of life, a stepping out of a dark tunnel and adjusting your eyes to the magnificence of creation. And then it ends with a subtle mix, a cacophony of life's highs and lows, an astoundingly complex interpretation of the human experience.
I always fail to find the right words to describe the pure majesty of this symphony.