Just read this article by A.J. Jacobs on giving effectively, it actually wasn't too helpful. I love his books, but his article, like most articles, didn't provide an answer. He did highlight some good resources though. There are groups that look into how to get the most out of your donation dollar, and this pursuit is called Effective Altruism (EA). Apparently some people really don't like these groups for various reasons. I can sympathize with both sides of the argument but I think the ones against Effective Altruism are the ones that are losing out. The Effective Altruism groups are a great resource trying to do good, the most good possible with the resources provided. The debate it really over the scoring criteria. I think the people against these groups need to embrace these groups and work with them on the scoring criteria. Possibly leave the weighting of the criteria to the person searching for a charity and simply provide a database of criteria and their ratings.
Here are some of the groups he mentions:
Herer's the article: