Nina Simone at the Harlem Festival, held in Central Park in 1969. According to Arthur Magazine the original film has been optioned but never released (they seem think it's a race thing). It's pretty amazing.
My (African-American) aunt Claudia once joked to me that she was pretty sure when she got to Woodstock and saw all the white people that she was the only one there to see Sly. According to this great Smithsonian magazine article, this bill also featured Stevie Wonder, Sly, Mahalia Jackson and Abbey Lincoln with Max Roach, among others. I don't think calling it the "black Woodstock" is out of the question.
Click through for the rest of Nina's performance.