Government websites
State Health Insurance Assistance Programs (SHIPs). These are state-run programs that can give you free, one-on-one answers to your Medicare questions. Here's the contact information for all SHIP programs.
Centers for Medicare and Medicaid Services
Medicare.gov. The official U.S. government web site for people with Medicare
Phone: 800-MEDICARE (800-633-4227)
Social Security Administration
Phone: 800-772-1213
Other websites
AARP(formerly the American Association of Retired Persons)
BenefitsCheckUp, a service of the National Council on Aging
My Medicare Matters, from the National Council on Aging