It's gotta be the Beatles. You could probably spend hours talking about how they changed music.
And I would give a nod to the Beach Boys as well. I've heard various artists refer to them positively. To tie it back to the prog thread believe it or not... I've heard the keyboardist of Genesis, Tony Banks, mention the Beach Boys in interviews before. Obviously musically it would seem a million miles apart, but I've seen him mention how the Beach Boys would do musically complex things and make them sound very simple, among other things. So you never know.