This, this, and this (summarized here). The poor in the U.S. are less poor than they used to be (and they are not, by and large, the same poor of a generation ago). Moreover, the poor in the U.S. are no poorer than the poor in the socialistic "paradises" of Western Europe and Canada. But the poor in the U.S. can become better off than the denizens of those other nations. And the chances of becoming better off are much greater in the U.S., given its superior economic performance.
Related posts:
Why Class Warfare Is Bad for Everyone
Fighting Myths with Facts
Debunking More Myths of Income Inequality
Ten Commandments of Economics
More Commandments of Economics
Zero-Sum Thinking
On Income Inequality
The Causes of Economic Growth
The Last(?) Word about Income Inequality
Now and Then, by Don Boudreaux of Cafe Hayek
More Data on Middle Class Americans, ditto
Half Empty or Half Full, Part I, by Russell Roberts of Cafe Hayek
A Kept Promise, by Greg Mankiw of the eponymous blog
A Primer on the Standard of Living and the Cost of Living, by Russell Roberts of Cafe Hayek
Census and Sensibility, by Jerry Bowyer at TCS Daily
Is the Increased Earnings Inequality among Americans Bad?, by Gary Becker of The Becker-Posner Blog
Why Rising Income Inequality in the United States Should Be a Noninssue, by Richard Posner of ditto