Pop stars - they've got the music in them. Marilyn McCoo was an R&B legend with The Fifth Dimension who became the host of Solid Gold. Before she moved to Knots Landing as Anne Matheson, Michelle Phillips topped the charts with the Mamas and the Papas. And Mandy Moore went platinum before she learned "How to Deal" with Zach Braff on Scrubs and Adrian Grenier on Entourage.—Peter Hays