Found the top graph via Paul Krugman’s blog. It is from a paper by Larry Bartels, professor of politics and public affairs at Princeton University.
{Click on the image to take a closer look}

I found a second graph in the same paper, showing the income inequality year to year (the 80/20 ratio measures the income inequality by dividing the income earned by someone at the 80th percentile by someone at the 20th percentile). Additionally, Bartels has highlighted the years Democrats and Republicans held the White House. Like a number of graphs on my site, you can see the increase in income inequality since the early 70s.
{Click on the image to take a closer look}

Data in the graphs are calculated from the Historical Income Inequality Tables compiled by the U.S. Census Bureau.
Addendum
5/2/08 Fix my definition of 80/20 income ratio
Technorati Tags: income, United States, inequality, Bartels
Popularity: 4% [?]
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From the New York Times

Technorati Tags: Happiness, United States, Income
Popularity: 7% [?]
I found this map of the world’s GDP Density via an Econbrowser post referencing an 1999 paper by John Gallup, Jeffrey Sachs and Andrew Mellinger.
GDP Density = GDP per capita * Number of people per square kilometer.
The darker the colors, the higher the GDP density.
{Click on the image to take a closer look}

Technorati Tags: population, income, World, GDP Density
Popularity: 89% [?]
Based on some comments on the United States Income Inequality Map, I am posting another United States Income Map, this time showing the Median Household income in the US by Census tract. I created it using a very cool tool: Social Explorer.
{Click on the image to take a closer look}

See also:
United States Poverty Map
United States Income Inequality Map
Addendum:
8/8/2007 Increased the size of the map legend.
8/19/2007 I added Alaska, Hawaii, and Puerto Rico to the map.
Technorati Tags: income distribution, US income distribution, inequality, income inequality
Popularity: 26% [?]
I found this Income Inequality Map posted at the Carsey Institute, U of New Hampshire.
After reading the article about the change in the Income Inequality in New England you can scroll down to find another map showing the low income population in Northern New England.
{Click on the graph to take a closer look}

See also:
United States Poverty Map
United States Household Income Map
Technorati Tags: income distribution, US income distribution, inequality, income inequality
Popularity: 28% [?]