The National Governors Association has a guide to Medicaid waivers. Many states are overhauling aspects of their Medicaid program as they try to restrain costs while expanding coverage, or as they develop community-based alternatives to nursing homes for the elderly and disabled. The NGA developed a tool kit for states going through the waiver process. The overview sections are written in ways that clearly explain the process and some of the trends at the state level.
The Kaiser Family Foundation has an issue brief that explains Medicaid waivers with particular attention to the six states that have done nontraditional Medicaid expansion.
State Health Care Spending on Medicaid: A 50-state study of trends and drivers of cost
National and State-by-State Impact of the 2012 House Republican Budget Plan for Medicaid
Why Does Medicaid Spending Vary Across States: A Chart Book of Factors Driving State Spending
Primer on Medicaid from the Center on Budget and Policy Priorities