CNNMoney.com currently has an article that compares how McCain & Obama's tax policies will affect people of different incomes. These are the summary conclusions:
McCain: The average taxpayer in every income group would see a lower tax bill, but high-income taxpayers would benefit more than everyone else.
Obama: High-income taxpayers would pay more in taxes, while everyone else's tax bill would be reduced. Those who benefit the most - in terms of reducing their taxes as a percentage of after-tax income - are in the lowest income groups.
The income distribution chart that was included in the article is attached as a jpeg.
Full CNNMoney Article:
http://money.cnn.com/2008/06/11/news..._tpc/index.htm
Tax Policy Center:
http://www.taxpolicycenter.org/aboutus/index.cfm