For me, it feels good to give. That is why I do it.
It is the best feeling for me when people tell me how happy something I have done makes them. Not just other charities, but my friends, family, co workers etc.
When I can go out of my way to do something for someone, when I can make something happen even though I have to get really resourceful and stay up late and not pee and not eat... well, that part kind of sucks... but when I can make a sacrifice to do something for someone else...
Well, it is the best feeling for me.
So it is selfish. (shhh! don't tell) It's more for me than for anyone else. Everyone else just gets a little bit of the happy that I feel.