The main funders are the William and Flora Hewlett Foundation, the David and Lucile Packard Foundation, the Oak Foundation, and the Rockefeller Brothers Fund. The Rockefeller Family Fund funds things south of the border. There's also the Wilburforce Foundation, the Brainerd Foundation, and the Bullitt Foundation. Those are the main ones.
The big five are Hewlett, Packard, Moore, Pew Charitable Trusts, and the Rockefeller Brothers Fund. Those foundations have $20 billion in assets and give away about $1 billion a year.