Mixtapes spread the hottest sounds, infringe copyright and break artists. Among them, 50 Cent polarizes, T.I. takes off with trap, and Lil Wayne clicks.

Auteurs like the Neptunes' Pharrell and Chad expand the sonic palette. Timbaland and Missy Elliott lean forward. Kanye West and J Dilla reimagine rap.

Innovators explode out of the South: Houston's DJ Screw slows hip-hop down, Memphis's Three 6 Mafia goes dark, and Atlanta's Lil Jon brings the crunk.

Rooted in New Orleans's rich music culture, No Limit mogul Master P and bounce breakouts DJ Jimi and Juvenile shake rap and put twerking on the map.