Don't forget state income tax, sales tax and various other embedded tax. Realistically, taxes are around 40% - 50%.
Also keep in mind that we get very little benefits for those tax dollars compared to Europe for example. Our healthcare costs and higher education are not covered by that tax the same way most European countries are. The only thing we do get for that money is perpetual war and bank/industry bailouts. Kind of a raw deal.
Preferably, I'd love to see a mixed system. A VAT tax, a flat income tax and capital gains tax. Something like 13/13/13 across the board (or maybe less if the US could get unnecessary spending down - not likely). This has worked brilliantly for several eastern European countries ever since they implemented them.