Forget Taxmageddon, Washington already has tax issues it is avoiding. Last year, Citizens for Tax Justice and the Institute on Taxation and Economic Policy issued a report on federal income taxes paid -- or not paid -- by large corporations.

Although the U.S. corporate tax rate is 35%, the study found that the average tax rate of the 280 S&P 500 companies investigated was only 18.5% between 2008 and 2010. Furthermore, 30 of the companies paid no net federal income tax in the same period. Now, the Citizens for Tax Justice has updated the report to reflect information for the 2011 tax year.

Twenty-six of the original 30 tax dodgers managed to keep a negative federal income tax rate after 2011 taxes were figured, meaning they still made more money after tax than before tax between 2008 and 2011. Three out of the remaining four companies paid four-year effective tax rates of less than 4%. The company at the bottom of the list paid a 2008 to 2011 tax rate of almost 11%.

As the report explains, "Had these 30 companies paid the full 35% corporate tax rate over the 2008-2011 period, they would have paid $78.3 billion more in federal income taxes. Or put another way, over the four years, the 30 companies received more than $78 billion in total tax subsidies."

Listed below are the 30 corporations with the lowest federal income tax rates on U.S. profits between 2008 and 2011, according to CTJ:

1. Pepco Holdings Inc. (POM): -39.5%
2. General Electric Co. (GE): -18.9%
3. PG&E Corp. (PCG): -18.4%
4. Wisconsin Energy  Corp. (WEC): -13.2%
5. NiSource Inc. (NI): -13.0%
6. Paccar Inc. (PCAR): -13.0%
7. Integrys Energy Group Inc. (TEG): -11.6%
8. CenterPoint Energy Inc. (CNP): -11.3%
9. Atmos Energy Corp. (ATO): -9.6%
10. Tenet Healthcare Corp. (THC): -8.2%
11. American Electric Power Inc. (AEP): -6.4%
12. Boeing Co. (BA): -5.5%
13. Ryder System Inc. (R): -5.4%
14. Con-way Inc. (CNW): -5.4%
15. Verizon Communications Inc. (VZ): -3.8%
16. Duke Energy Corp. (DUK): -3.5%
17. Interpublic Group Inc. (IPG): -2.5%
18. NextEra Energy Inc. (NEE): -2.0%
19. CMS Energy Corp. (CMS): -1.4%
20. Navistar International Corp. (NAV): -1.3%
21. Consolidated Edison Inc. (ED): -1.3%
22. Mattel Inc. (MAT): -0.9%
23. El Paso Corp. (EP): -0.9%
24. Baxter International Inc. (BAX): -0.6%
25. Apache Corp. (APA): -0.3%
26. Corning Inc. (GLW): -0.2%
27. DTE Energy Co. (DTE): 0.2%
28. Honeywell International Inc. (HON): 2.0%
29. Wells Fargo & Co. (WFC): 3.8%
30. DuPont Co. (DD): 10.9%

According to the CTJ  study, corporate taxes made up only 1.2% of our gross domestic product over the past three fiscal years. "That's lower than at any time since the 1940s," the study notes, "except for one single year during President Reagan's first term." In the 1960s, by contrast, corporate taxes made up almost 4% of GDP.

Eric McWhinnie is an editor at Wall St. Cheat Sheet. As of this writing, he did not own a position in any of the aforementioned stocks.

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