http://www.irs.gov/pub/irs-soi/06in11si.xls
It's interesting that people making between $100,000 and $200,000 pay the majority of collected taxes, 20.4%. Sure people making more money pay more percentage wise of their taxable income, it's just there are so many more people in the 100 to 200 thousand tax bracket that they bear the most weight of the total taxes collected. So the upper middle class contributes the most. I love Wikipedia but you have to fact check it because anyone can go in and edit the information.