The Center for Budget Policy Priorities posted a guide to historical trends on Income Inequality. Clearly, income inequality has been growing since the 1970s, returning to a level not seen since the Great Depression (1929). See the full report: Click Here
Among the many charts and tables, I think these two are very interesting.
One shows a comparison between income distribution and wealth distribution:
The second shows the distribution of income before and after taxes. There is a redistributive effect, but not as much as I assumed there would be: