Taxes are a primary tool for redistributing income from the wealthy to lower income earners. The economic impact of the redistribution of income is a highly debated topic and arguments are generally formed in the Tax Reduction/Increase debates. The following two sites look at world income distribution and provide a comparison over time

http://www.globalpolicy.org/social-and-economic-policy/global-injustice-and-inequality/inequality-of-wealth-and-income-distribution.html

http://www.imf.org/external/pubs/ft/weo/2007/02/

Data for the U.S. are also available from the Census Bureau at: http://www.census.gov Search for income distribution. From the Heritage Foundation, a conservative think tank, there are two articles that address the impact of tax changes:

http://www.heritage.org/Research/Budget/wm1639.cfm

http://www.heritage.org/Research/Budget/wm1648.cfm