A Good Cause - 100 million by any chance?

Every year, I donate to a charity before Christmas, as many people do. I have tried to get my family to do this instead of buying (always far too many) presents, but have failed. I today read that an individual had donated UsD 100 million to New York's Central Park. There's a billionaires club, of which I think Gates and Buffet are party, trying to encourage others with similiar means to use half of their assets for a worthy cause. It's often more (or entirely) symbolic at my income level, but I find it important to think about those not as priviledged as us, with a practical contribution, at least this one time a year. I'd be happy to receive suggestions for this year's cause. Inspire me with a link or organization to look into. (Apologies for festive season thoughts two months ahead of the time. The UsD 100 million donation just made me think of this.)