Carrie Underwood, Justin Bieber, Cee Lo Green and LMFAO have been announced as a few of the artists tapped to perform at the upcoming Billboard Music Awards, scheduled to take place May 20th at the MGM Grand in Las Vegas.  Organizers for the awards ceremony, which will air live on ABC television, also announced that it will be hosted by Julie Bowen and Ty Burrell, the co-stars of the sitcom "Modern Family."