The Urban Institute's Tax Policy Center has a nice whiteboard video explaining who pays no federal income tax. The tone is liberal, but it is factually accurate. (I have not double-checked their facts, but it is consisent with my recollection of the facts.)
The video omits two important issues: one is the disincentive effects of our tax system, and the second is the ethical issue: should anyone be relieved of a responsibility to support the government?