Since the '90s, Ben Harper has been nothing but restless, carrying his guitar and those soulful pipes through nearly every conceivable genre. As effortlessly as he performs solo, he's even more adventurous as a collaborator, battling Charlie Musselwhite's wild harmonica, stomping through jaunty folk rock with Fistful of Mercy, and stirring up a simmering Bob Marley cover with Jack Johnson.