Peter R. Merrill (PricewaterhouseCoopers, Washington, D.C.) has published Competititve Tax Rates for U.S. Companies: How Low to Go?,122 Tax Notes 1009 (Feb. 23, 2009).  Here is the abstract:

This article concludes that to match the average top statutory corporate tax rate in the other 29 OECD member countries, the U.S. federal corporate tax rate (taking into account state income taxes) would need to be reduced from 35% to between 21% and 25.5%, where the lower benchmark is a simple average and the higher benchmark is GDP-weighted. This range is less than the 28% corporate tax rates that Chairman Rangel reportedly is considering for his new comprehensive income tax reform bill. The article also finds that effective tax rate calculations, which take into account both the tax base and tax rate, show that the U.S. corporate tax burden is quite high by international standards. The benchmark tax rate relevant for competitive taxation of the foreign-source income of U.S. multinationals (19%) is considerably lower than the average OECD tax rate.