Healthcare Cost and Utilization Project (HCUP) (US Department of Health and Human Services, Agency for Healthcare Research and Quality) - provides data on "hospital utilization, access, charges, quality and outcomes."
Fair Health- free resource that is dedicated to sharing healthcare prices and health insurance information. Its cost lookup tool allows you to estimate costs of medical and dental services in specific areas of the United States. The cost estimates are based on Fair Health's national database of healthcare claims.
Healthcare Bluebook is a commercial website that provides cost estimates for medical procedures, tests, and services to consumers, employers and providers.
Health Care Cost Institute - publishes the annual Health Care Cost Report and the National Chartbook of Health Care Prices, as well as other relevant reports.
guroo - a website created by the Health Care Cost Institute, it gives data on health care costs and quality with national, state and local prices.
State Health Facts (The Kaiser Family Foundation) - health statistics for each state including health costs, health coverage, health reform, health status, Medicaid, Medicare, minority health, women's health
Kids Count Data Center (Annie E. Casey Foundation) - data on child and family well-being in the United States, including health metrics
ICPSR Data Archive (Inter-university Consortium for Political and Social Research) - a data archive for social and behavioral sciences. One of the thematic collections is "Health/Mental Health" which includes data sets for chronic health conditions, LGBT health, aging, etc.