Folk trailblazer Joan Baez spurred peers like Bob Dylan and Joni Mitchell to excel, though her impact extends generations after her '60s heyday. Her social-justice politics inform the protest songs of Tracy Chapman and Indigo Girls, while her dusky marvel of a voice is an antecedent for everything from Laura Marling's spare ballads to Shawn Colvin's mellow pop and Norah Jones' jazz-inflected twang.