Social Security Administration (SSA)
By its nature, this site offers a variety of material for
employers, employees, and beneficiaries. However, there is
substantial statistical information from the "Office of Research,
Evaluation and Statistics (ORES)" and the "Office of the Chief
Actuary." The former includes the "Current Operating Statistics
Tables" (with everything from the trust funds, to current benefits
to black lung benefits), income maintenance programs, economic
indicators, beneficiaries by county, and studies on
disability programs. The latter includes data on the financial
aspects of the Trust Fund, and beneficiary data, as well as other
material.
http://www.ssa.gov/