This definition of social policy from the Dictionary of Sociology, may help clarify what a policy is, and how it's different from a plan or a program that implements a policy.
The Green Book (in progress) is a FANTASTIC resource for federal programs. It provides updated statistics and information on programs such as Medicare, Social Security, Unemployment Compensation, Foster Care and welfare. Additionally, it includes a discussion of related issues, such as the well-being of the elderly and of children and families. (If the program you're interested in hasn't been updated yet, you can also try the 2004 Green Book.)
LexisNexis Congressional contains congressional documents (hearings, committee prints, documents, and legislative histories) which are searchable through this fulltext database.
Polisphere a very helpful custom search engine -- lets you search the web for policy related issues, and you can refine your search by limiting it to policy organizations, or federal, state, or local government.
LexisNexis Government Periodicals Index Indexes over 170 periodicals published by agencies of the US Government.