Try
http://www.taxpolicycenter.org/TaxFacts/international/gdp.cfm for the tax burden of the OECD countries. The figures are for 1999, so will have changed a little by now; note that developing countries (eg Mexico, at 16%) tend to have a low tax burden, and you may or may not consider it a relevant comparison. But Japan, in 1999, had a slightly lower burden than the USA: 26.2% v. 28.9%. Other OECD countries are higher than the USA.