Follow the example of Facebook billionaire Dustin Moskovitz. In his words: "I never viewed money as being ‘my money.’ I always saw it as ‘The money.’ It's a resource. If it pools up around me then it needs to be flushed back out into the system. . . . All that said, it turns out to be quite difficult to flush such a large sum back into the world in a way you can feel confident about, which is why we started Good Ventures and work so closely with GiveWell."

I would encourage you to contact GiveWell directly (Contact Us | GiveWell), introduce yourself as a potential major donor, and ask them for advice on how you can save the most lives or make most difference you can with several million dollars.

For more about effective altruism, check out Peter Singer's TED talk: The why and how of effective altruism.