You might want to look at Visage (http://visagepayroll.com http://visagepayroll.com), which I think was first in the "free payroll" market; their revenue stream

You might want to look at Visage (http://visagepayroll.com http://visagepayroll.com), which I think was first in the "free payroll" market; their revenue stream comes from Credit Karma-style financial product targeting, but all the payroll features are free. (No affiliation, but I've run into their CEO in the past and he's a very solid guy.)