Tax Loopholes

Does anyone have a very good, solid source (more than one is great) for what kinds of tax loopholes corporations are using to avoid paying back into our society? I know about billionaires putting their taxable address in the Cayman Islands for example, but that's the only one in particular, and I'm looking for corporations, not people.

Thank you so much. This information will be useful in general, but at the moment I'm looking forward to arming myself with it while dealing with my mother.

I was raised watching Bill O'Reilly with dinner -.-