The Giving Pledge, or the commitment to give away at least half of one's wealth to charitable causes, has become a very exclusive list of the "who's who" of billionaires.

Formally announced in June 2010, within the first two months the pledge had received commitments of more than $125 billion from 40 wealthy donors. Since then, the pledge has grown to more than 125 billionaires, all of whom are committing to donate at least half of their wealth, and some are going way beyond that.

For example, Warren Buffett has pledged to give nearly all of his fortune away, with the vast majority going to the Bill and Melinda Gates foundation, who are also giving away most of their wealth. The exact amount Buffett has pledged is 99% of his net worth -- which based on his net worth today according to Bloomberg, is roughly $65 billion.

Here is a sampling of the most well-known billionaires who have committed to giving the majority of their wealth away, in no particular order.