I'm looking for some good examples.

It can change the entire mood of a song.

I have literally stolen the idea of this thread from this guy:
http://www.neogaf.com/forum/showthread.php?t=436932

Which lead me to this fantastic cover of Nirvana.
http://www.youtube.com/watch?v=C0dwfRt8LcI

But those guys are mainly gamers. You're all meant to be music folk, so enlighten me.