From the Tax Foundation
IRS data shows that in 2007—the most recent data available—the top 1 percent of taxpayers paid 40.4 percent of the total income taxes collected by the federal government. This is the highest percentage in modern history. By contrast, the top 1 percent paid 24.8 percent of the income tax burden in 1987, the year following the 1986 tax reform act. Remarkably, the share of the tax burden borne by the top 1 percent now exceeds the share paid by the bottom 95 percent of taxpayers combined.
N.B.: These percentages reflect both changing tax policy and the changing distribution of income.