Checkout GiveWell (http://www.givewell.org/ http://www.givewell.org/). They are ex-hedge-fund guys who wanted to apply quantitative methods to this very questio

Checkout GiveWell (http://www.givewell.org/ http://www.givewell.org/). They are ex-hedge-fund guys who wanted to apply quantitative methods to this very question. Also, from a personal standpoint, I try to give in accordance with Peter Singer's recommendations that you should help the worst off first (So things like Malaria Nets and de-worming). It's easier to be sure you're making things better if the money goes to treating a life-threatening disease that can be prevented for a few dollars a head.