From www.irs.gov website:  IRS Tax Tip 2012-25: 
Although most income you receive is taxable and must be reported on your federal income tax return, there are some instances when income may not be taxable.
The IRS offers the following list of items that do not have to be included as taxable income:
Adoption expense reimbursements for qualifying expenses
Child support payments
Gifts, bequests and inheritances
Workers’ compensation benefits (some exceptions may apply; see Publication 525, Taxable and Nontaxable Income)
Meals and lodging for the convenience of your employer
Compensatory damages awarded for physical injury or physical sickness
Welfare benefits
Cash …