Is there somewhere I can check the reputability of a charitable organization before donating to them? Also, how do I find out how much of my money is going to the mission of the organization and not just "administrative costs"? Is that public information?
Dear Sadie - Eve's advice is spot on. Charitynavigator is a great place to start gathering information. Public charities are required to disclose financial information on Form 990 for their most recent fiscal period. You should review the Form 990 data and use it to formulate additional questions. Well-run charitable organizations love to talk about what they do, how they use their funds, and how new gifts can make an impact on their mission.
If you do not receive a favorable reception when you make inquiries, then I would counsel that you look at other charities.
You can go to charitynavigator.org. Many, but not all charities are found there. And, public charities must release their financial information, however some others (religious charities, for example) do not. You can also ask the charity you're interested in for their financial reports. If they don't provide them to you, then that might give you a reason to look elsewhere.
Many people have listed charitynavigator.org and this is a great resource. There are others out there as well including guidestar.org, charitywatch.org (this one is a paid subscription, i think), and foundationcenter.org/ (this one will give you a lot of technical information and not necessarily the ratings of charity navigator or guidestar. It is used a lot by the charities themselves to find grants, etc.)