One of the few megastars only needing a single name, Madonna's brand of dance pop began as the purest of bubblegum but has become increasingly sophisticated during the course of a career now in its third decade. Her influence has lessened a bit since the multimedia dynasty she lorded over in the 1980s and early '90s, partly because she's been busy raising children and partly because the focus of dance-oriented music has radically shifted in the years between Bedtime Stories (...  [+]