At the American Payroll Association's annual meeting in May, Lisbeth Green's workshop on payroll cards drew a standing-room-only crowd of 230 people. "That shows you the interest [in payroll cards]," says Green, president of payroll consulting firm L.K. Green & Associates in Santa Clara, Calif. "It's growing every single day."

Why bother with pay cards when there is direct deposit? Despite the big savings possible with direct deposit, only about 60% of U.S. employees are paid that way, says Green, and about half of the workers who aren't simply don't have bank accounts.

That challenge has led companies to consider payroll cards, which work whether an employee has a bank account or not. The corporate advantage: It's cheap. Where cutting a check can cost between $3.50 to $4 per check, a payment via payroll card is estimated at $2.