Beethoven's 14th Sonata, the "Moonlight Sonata" third movement. Since I'm going crazy trying to find a good version of this on YouTube and finding none, I said screw it and uploaded this version of it.
This version, by Vladimir Ashkenazy, is my favorite version of the song and the best version of it that I've ever heard. I've heard so many versions of this song, but I always come back to this one. He puts a great final touch on the sonata with his third movement, which is incredibly powerful.