In place of dollars, a cool change  Cash has never been so cool. Usher Raymond IV, the 25-year-old R amp;B singer who has been dubbed the king of pop, launched the Usher Debit MasterCard late last month. The sleek black card, which features the artist's face, has been passed out to concertgoers during his nationwide ''The Truth Tour. quot; The card is also available through a website, ushermc.com.