"Pop music would be a different beast without the B-Side. Music history is riven with songs deemed throwaway that revolted against their lowly status and refused to be denied. Be it rock'n'roll's national anthem ('Rock Around The Clock'), disco's enduring game-changer ('I Feel Love') or hip-hop's most notorious dis track ('Hit 'Em Up'), all three started life as the so-called 'lesser' track on releases primed for maximum chart impact. But the B-side...