Please visit GiveWell.org This CharityScorecard.org site was in use from 2006 to 2008, but is now mostly dormant, and the material here is out of date. The GiveWell project has similar goals and is being actively maintained. I've left the old CharityScorecard.org content here just for the historical record.

From CharityScorecard

United States dollar (USD or US$) 

The dollar is a unit of currency in the US. Within the US, dollar figures are is commonly abbreviated using the $ symbol, but the $ symbol can be ambiguous because different dollars are used as units of currency in many countries. The Charity Scorecard site also has pages which include figures in International Dollars (Int$). To avoid confusion, we've tried to avoid using the $ symbol by itself, and instead use US$, USD, or Int$. See also: http://en.wikipedia.org/wiki/United_states_dollar