Center for Law and Social Policy (CLASP) "CLASP's mission is to develop and advocate for policies at the federal, state and local levels that improve the lives of low income people." CLASP is an excellent source with a very well organized web site. CLASP is a public interest law firm.
The National Conference of State Legislatures is a bipartisan group of state legislators and their staff. The NCSL web site provides research on policy and issues from the state perspective. Some content is resticted to members of the NCSL, but there is a lot of good information that is available to the public .
The National Governor's Association is source for policy research from the state perspective. The NGA Center for Best Practices and the Federal Relations sections of the web site are good starting points. Notice that these sections are further divided by issues.
The U.S. Conference of Mayors is an organization for cities with populations greater than 30,000. Each city is represented by its mayor. Extensive information regarding urban policy.