Mariah Carey, Beyonce, Usher and 50 Cent are among the artists being pressured to return money received after performing for Libyan dictator Muammar Qaddafi and his family members, RollingStone.com reports. Carey reportedly was paid $1 million to sing for Qaddafi's son, Muatassim, Libya's national-security adviser, at a New Year's Eve party on St. Barts in 2008. 50 Cent performed for Qaddafi's son in 2005, and Beyonce and Usher performed at a party in 2009 -- all for undisclosed sums of money. "If it were me, it would go to charity," Buck Williams, agent for R.E.M. and Widespread Panic, told Rolling...