Known as TV's most unlikely hipster, Canadian-born Paul Shaffer has served as David Letterman's music director and sidekick since "Late Night with David Letterman" first aired on NBC in 1982. A marvelous foil for Letterman's humor and a consummate popular musician whose keyboard virtuosity enables him to collaborate with virtually any performer, Shaffer moved with Dave to CBS in 1993, and his groovy patter and eclectic music have helped "The Late Show with David Letterman" maintain its cutting-edge gloss through the years. In addition to his own albums, "Coast to Coast" (1989) and "The World's