When you have a voice as velvety and versatile as Akon's, it's easy to understand why artists from 50 Cent to Snoop Dogg have his number on speed dial. Akon became hip-hop's hook man du jour following his 2004 platinum debut, Trouble. And demand for his catchy choruses quickly grew following his contribution to Young Jeezy's 2005 street anthem, "Soul Survivor." Dig this mix of Akon's best guest appearances.