An interesting GAO study about what corporations (both domestic and international) pay in taxes in the U.S.
Key Quote:

The Government Accountability Office said 72 percent of all foreign corporations and about 57 percent of U.S. companies doing business in the United States paid no federal income taxes for at least one year between 1998 and 2005.

Keep in mind that these are the same corporations to which the GOP wants to give additional tax breaks. Something is fundamentally wrong here.