Strengthen the Earned Income Tax Credit Act of 2007 - Amends the Internal Revenue Code to: (1) make permanent the reduction in the marriage penalty applicable to the earned income tax credit; (2) increase the rate of such credit for families with three or more children; (3) increase the rate and the phase-out percentage of such credit for individuals without children; and (4) make permanent provisions treating combat pay as earned income for purposes of calculating such credit.