The Center for Poverty Research annually updates our state level panel data series covering population, employment, unemployment, welfare, poverty, and politics. The UKCPR National Welfare Data begin in 1980 and the excel file may be downloaded free of charge.
This dataset was produced as part of my project with Robert Moffitt "Block Grants and the Welfare State," which was generously funded by the Russell Sage Foundation. The data are a state-by-year panel containing detailed information on welfare program expenditures and recipiency, along with other economic, policy, and demographic characteristics at the state-by-year level. The data are available as an Excel file here and the associated code book is available here.
State-by-Year Effective Tax Rates in the AFDC/TANF Program from 1983-2002 are available to the research and policy community. These rates were estimated in my 2007 paper "Making Work Pay" in the Journal of Human Resources.