Oh, man, that scene utterly blew me away in the movie. And it really threw me for a loop; I wasn't expecting it at all. I thought he might sing, but not like that. And I read that was a last-minute addition too; Jackson thought the charge scene needed something, so he decided it would be a good place to insert a song. It really turns what could have been just a horrific scene of mass slaughter into a very intimate moment of melancholy. It's a defining moment for Pippin, as well as a way of getting the audience to appreciate the loss on a more personal level. The track is "The Steward of Gondor," and the words are the last verse in a song that shows up early in the first book. It's another example of how the filmmakers take things directly from the book and place them in a completely different context, to dramatic and surprising effect. They did that a lot with Pippin in "Return"; another really powerful moment was his conversation about death with Gandalf. Gandalf's words were largely lifted from the narration at the very end of the book; I thought that little conversation was a stroke of genius. Anyway, the song is referred to in the book as "Upon the Hearth the Fire is Red" or simply a Hobbit Walking Song and is supposed to have been written by Bilbo. I agree, Billy's voice is divine, and the fact that he composed the melody himself is very impressive. Erm... sorry about the rambling... Did I mention I love your new avatar???
Erin