The National Center for Health Statistics (NCHS) is the main clearing house for US health statistics. Their goal is to provide information to inform decisions on public health and health policy. Detailed information on aspects of the US healthcare system is available here.
The American Hospital Association (AHA) is a trade organization and advocacy data that represents many US hospitals. They conduct an annual member survey and present data on hospital expenditures and usage as part of their advocacy role.
The Organization for Economic Co-operation and Development (OECD) is an intergovernmental organization with 38 member countries. They collect and distribute health data to improve the quality of international comparisons and economic analysis.