I found a couple of websites that kind of show some of this:
A few causes listed on Give Spot
Celebrities for Awareness
but not really a comprehensive list.
I also found some articles on whether celebrity giving is a positive or negative, or both:
CNN discusses it
Associated Content's take
So, question: What do your favorite celebs support, if anything? Why did they decide to do it? What do they do or give? Any other thoughts on this? (Or any other websites that highlight celebrity giving?)