No disrespect intended to the OP but it's impossible for me to list the best song ever. I tend to like music from lots of different genres so it probably changes day to day. One day might be Take Five by Dave Brubeck and the next day might be Comfortably Numb by Pink Floyd. Who Knows???
Anyway, there are a lot of great songs listed but here are a couple of my favorites...for today anyway!
[ame="http://www.youtube.com/watch?v=RaW2_LMEEz8&feature=fvst"]YouTube - Roger Hodgson "School" (Supertramp) - Showing visually the complex L and R ch phase relationship[/ame]
Performed the way it should be and not like the Faith Hill cover. Not that I don't think Faith Hill has some decent songs but definitely not this one.
[ame="http://www.youtube.com/watch?v=ApfKglyNjyA"]YouTube - Take another little piece of my heart[/ame]
and of course Marvin Gaye
[ame="http://www.youtube.com/watch?v=y-5c5o85SGo"]YouTube - Marvin Gaye "Whats Going On" (1971)[/ame]