www.taxfoundation.com is a great site for tax policy analysis.
For example, here is the Income Tax breakdown for 2006.
Among the highlights, the Top 1% now pay 40% of income taxes, despite only earning 22% of income. The Top 50% now pays over 97% of income taxes. If you earn over $32,000, you are in the Top 50%. If you earn over $65,000, you are in the Top 25%.