UPDATE – Intuit discontinued this app on December 31, 2014.
Intuit has just launched Intuit Snap Payroll. It is a free simple app for the iPhone and iPad for calculating the payroll for your employees.
Note that this is a very basic payroll calculation app so will only be suitable if you have a limited number of employees and those employees have very straightforward payroll situations. Anything more complicated will require a different payroll solution.
As of the date of this posting the app is available for payrolls operating in 12 states with more to follow. To see if your state is included go to the Intuit Snap Payroll web site.
Charlie Russell at the Sleeter Group has posted a good overview of the app together with screen shots.