Here are two YouTube videos by Public enemy and a link to an article from googlescholar about revolutionary hip-hop

http://www.youtube.com/v/CuTi9UZtPbw&hl=en

http://www.nodo50.org/cubasigloXXI/congreso04/haworth_290204.pdf

http://www.youtube.com/v/dvOd48zlNkA&hl=en