There are many organizations focused on LGBTQIA+ legal issues. Depending on the organization, researchers might find a wealth of information including multi-state surveys, reports, papers, and self-help guides.
These organizations vary from legal advocacy groups to research/policy think tanks. For any organization, look at the mission or the "about us" section to determine the purpose of the group and funding sources. While information on these sites can be very useful, be aware of any bias in their analysis--advocacy groups are advocating for a cause and think tanks might have a certain research agenda.
There are many regional organizations that focus on LGBT law. These include BALIF (San Francisco) and Sylvia Rivera Law Project (New York City).