[ABV]

Average Tax Rate (% of AGI paid in income taxes) 2003
Top 1% - 24.31%
Top 5% - 20.74%
Top 10% - 18.49%
Top 25% - 15.38%
Top 50% - 13.35%
Bottom 50% - 2.95%

Any way you look at it, the more money you make, the more taxes you pay.

Here's some more info for reference:
Minimum AGI for tax return to fall into a given percentile (2003).
Top 1% - $295,495
Top 5% - $130,080
Top 10% - $94,891
Top 25% - $57,343
Top 50% - $29,019