20. Demi Lovato
After weathering a well-cataloged meltdown, a stronger, wiser Demi Lovato emerged in 2011 with a successful comeback album and a fierce new attitude. This fall, she'll take her career to the next level as a judge on "The X Factor" alongside another diva who knows a thing or two about reinvention: Britney Spears.—Jeff Royer
(Photo: Paul Marotta, Getty Images)
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