I also think Tom Hanks and his wife Rita Wison contribute much, but keep it quiet. Obviously Brad Pitt and Angelina Jolie do much, and I can only imagine how much they contribute. Matt Damon is another great guy, he is using his celebrity to bring awareness and trying to get clean water for the world (something many of us take for granted) Water.org
I am sure there are so many celebrities and athletes that contribute so much and don't get recognition because they don't want it to be about them. If I was uber rich, I would be the same way... I would want to help people because I could, not for attention. That is why some of the celebrities or pop stars that act up all the time are so annoying... they are so blessed, yet they could do so much good with their fortune instead of taking it all for granted and wasting it.