Individual donors to presidential candidates can contribute up to $2,500 for the state-by-state party nominating contests and another $2,500 for the general election. But independent groups called Super PACs have no limits on what they can raise from individuals, corporations or labor unions.

Here is a look at wealthy individuals who have contributed at least $1 million to the major "super" political action committees as disclosed to the Federal Election Commission.

RESTORE OUR FUTURE

Total raised as of September 30: $110.5 million

(Supports Republican presidential candidate Mitt Romney)

PRIORITIES USA ACTION

Total raised as of September 30: $50.1 million

(Supports Democratic President Barack Obama)

AMERICAN CROSSROADS

Total raised as of September 30: $68 million

(Supports Republican candidates for federal offices)

(Reporting by Patrick Temple-West, Alexander Cohen and Alina Selyukh; editing by Todd Eastham)