If you were inspired by Warren Buffett's recent 31 billion dollar donation to the Gates Foundation, but aren't sure which charity can do the most good with your donation, check out Charity Navigator. The site offers detailed data for thousands of charitable organizations, including their mission statements, executive compensation, and efficiency in resource allocation. This is a great resource, especially considering that the charities you hear the most about tend to be the ones whose budgets focus disproportionately on marketing rather than on helping people.
http://www.charitynavigator.org