On June 28, 2012, the U.S. Supreme Court upheld the Patient Protection and Affordable Care Act [PPACA], but made the expansion of Medicaid included in the PPACA optional.  
In the months since, states have grappled with the question of whether or not to expand Medicaid coverage to include all adults up to 133 percent of the poverty level.  The Advisory Board Company, a health care consulting firm, has a frequently updated interactive map showing where each state stands.
A number of recent articles have discussed the issues involved:
Although much attention has focused on state governors, legislation will be needed to implement changes in states' Medicaid programs. 
The National Conference of State Legislatures [NCSL] has a searchable database of pending legislation related to the PPACA which can be used to track legislation related to Medicaid expansion:
You can use Texas Legislature Online to find bills filed during the 83rd Legislature about Medicaid.
NCSL's Health Reform Information pages include a wide range of other documents related to state implementation of the PPACA .