If you spend any time on a subway or at an airport you'll see Beats-branded headphones all over the place. The high-end headphones, released in 2008, are the creation of acclaimed hip-hop producer and rapper Dr. Dre. The underlying technology is now also being used as audio components for branded H-P ( HPQ) laptops and the HTC ( HTC) smartphones. Dre is far from the only hip-hop artist who has struck gold as a businessman. 50 Cent pulled down a quick $100 million after Coca-Cola ( KO), bought Glaceau, the maker of Vitamin Water, for $4.2 billion in cash in 2007; he'd earned an ownership share through a 2004 endorsement deal. Akon's "bling" is actually from a diamond mine he owns in South Africa. In 1998, P. Diddy started a clothing line, Sean John, and has since launched a fragrance and restaurant chain and inked a variety of endorsement and marketing deals.