Who? The first-ever (and still-biggest) Idol victor.
Peak: Second album, Breakaway, went platinum six times and spawned several monster singles including "Since U Been Gone," "Behind These Hazel Eyes" and the title track. Her latest LP, All I Ever Wanted, debuted at Number One in March '09 and is still going strong.
Low: An ill-conceived public feud with label boss Clive Davis in 2007, followed by the cancellation of an arena tour and a cooler reception for third LP, My December (which has since gone platinum).
Currently: Her fifth studio album, Stronger, a self-described mix of “Prince, Tina Turner, Sheryl Crow, Radiohead,” sprinkled with country influences and produced by Gaga-and-Beyoncé-approved Darkchild, hit stores in October 2011.