Couple of good ones

Nas - VH1 Driven
http://www.youtube.com/watch?v=piwELZZVn-U

Gil Scott Heron Godfather of Rap
http://www.youtube.com/watch?v=-kdevhUCn7o

The Real John Lennon
http://www.youtube.com/watch?v=X0uQlxCx89U

Not a full length documentary.but it tells the story of illmatic.

Nas - illmatic EPK
http://www.youtube.com/watch?v=7MEp-VaI1-k

Stevie Wonder - Documentary 1980 Hotter than July
http://www.youtube.com/watch?v=MnccZm4uw_M

Not Youtube but oh well

One of the best hip hop doc's i've ever seen.

Scratch Documentary (2001)

http://dai.ly/bbpK8Y

Scratch is a documentary film, directed and edited by Doug Pray. The film explores the world of the hip-hop DJ. From the birth of hip-hop, when pioneering DJ’s began extending breaks on their party records (which helped inspire break dancing and rap), to the invention of scratching and beat-juggling vinyl, to its more recent explosion as a musical movement called turntablism, it’s a story of unknown underdogs and serious virtuosos who have radically changed the way we hear, play and create music. The documentary opens with Grand Wizard Theodore (New York) telling the story of how he first introduced scratching. Throughout the documentary, several artists (like Afrika Bambaataa, Mix Master Mike, QBert, DJ Shadow, Cut Chemist and many others) explain how they were introduced to the field of hip-hop and scratch while providing stories and anecdotes of their personal experiences.