One Direction

By August 2015, 1D will have reached the half-decade mark. That's dangerously close to the expiration date for boy bands. Backstreet Boys, N Sync and New Kids on the Block all rode the hormonal wave for four years before an ever maturing fanbase dropped their popularity off a cliff. That explains why tickets for their concerts go on sale nearly a year in advance: Hook 'em while they still care.