He only had a few hits in the 1950s and early '60s, but as Bo Diddley sang, "You Can't Judge a Book by Its Cover." You can't judge an artist by his chart success, either, and Diddley produced greater and more influential music than all but a handful of the best early rockers. The Bo Diddley beat -- bomp, ba-bomp-bomp, bomp-bomp -- is one of rock & roll's bedrock rhythms, showing up in the work of Buddy Holly, the Rolling Stones, and even pop-garage knock-offs like the Strangeloves' 1965 hit "I Want Candy." Diddley's hypnotic rhythmic attack and declamatory, boasting vocals str...