In 2003, Britney was five years and four albums into her career. A lifetime for some pop musicians, Britney needed to do something to establish her staying power. All it took was some synth, a bevy of strings and a Bollywood beat, and voila, Britney had Toxic. Possibly her best contribution to the pop music world, Toxic shot new life into Spears discography and was the ultimate put-off to critics accusing her music of sticking to formula. It was new, aggressive and undeniable, becoming her biggest hit in the process. Its the quintessential millennial pop song: a simple verse-to-chorus progression, a built-in dance break, and a hook that goes on for days. Later that decade, the song would find itself placed time and time again on Best of the Aughts lists, and the central message was clear: pop music should always be this exciting. Do you agree with this run-down of Britney's classic tunes? Share your own thoughts below...