Allison Iraheta, Kris Allen and Sean Kingston performed at our Billboard New Year's Live show in Las Vegas while Christina Aguilera and Pete Wentz popped champagne across town. Mariah Carey helped her fans ring in 2010 at Madison Square Garden. Adam Lambert held court in Hollywood. And Black Eyed Peas, Jennifer Lopez, Justin Bieber, Daughtry and more rocked the masses across the country. It all happened on New Year's Eve 2010 -- and we've got the pics to prove it.
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