I would like to make a donation
I would certainly be okay with this as a money sink, one that would probably work rather well. Ad some badges to it, and it would be complete. I know one guys who would gladly throw billions at it if that's what it takes to collect all the badges for his main toon.
Great ideas all around here. I'll +1 every one of them. Badges for giving to charity NPC's, charity missions, all that stuff is great. A hero really should be able to do such things and not just beat bad guys.
It may be cool if there were some charities created in-game, and the hero could select to donate to specific ones. Then those which get more inf will develop with time into more respectable ones, or possibly into big and corrupt organisations which the hero will then have to fight.
We've been saving Paragon City for eight and a half years. It's time to do it one more time.
(If you love this game as much as I do, please read that post.)