I spoke earlier about maximizing the value of your charitable donations by choosing your charities, wisely. Charity Watch is an organization that helps to do that by ranking charities based on how much of what they take in is spent on directly helping people, vs. how much is used in running the charity or in soliciting donations.
That's an imperfect measure, of course. Just giving every penny that comes in directly to the targeted beneficiaries is not necessarily the best way to do good works. Some management can make the charity more effective. And investing in driving future donations is useful to, though in many cases non-profit groups are just competing against each other for peoples' hard earned dough. But it is a good jumping-off point when trying to figure out a group that has come to you, hat in hand.