This might be a great plugin for the browser: Install it, have it display ads on either all (charitable) sites to pay out to the specific sites, a specific charity or have adverts only on specific sites. Kind of like a reverse adblock.

humancredit tries to set up a network to do something like this. The system they want to create is a bit more complex but if it scales it might move a big chunk of money.

Basically advertisers pay for a seal that means that their advertising supports a good NGO. Users can install a browser plugin and vote on ads they are shown (this gives advertises additional data that they want to pay for) and vote towards which foundations the money get's donated.

*Disclosure: Once of the guys behind the project is a Facebook friend of mine.