The preeminent scholarly organization for the field. it also publishes the journal American Quarterly along with hosting annual meetings and conferences. There are numerous regional chapters for the organization and it also gives out numerous awards and grants to scholars (and students) in the field. The association also maintains a listing of jobs, calls for papers, and fellowships.
The regional chapter which William & Mary resides within, it covers the states of Virginia, West Virginia, North and South Carolina, Georgia, Alabama, Mississippi, Louisiana, and Florida. It hosts a regional conference every other year along with providing awards and travel grants to graduate students.
The IASA's website is a bit less polished and not as well-maintined or updated as the ASA's, but it is still a recognized and respected international body within the field. It hosts biennial conferences along with publishing the Review of International American Studies.
This post on the blog for the Society for U.S. Intellectual History came from a panel that the author participated in at the 2013 Society conference. The post is in line with many of the current trends in American Studies, but also looks more closely at the current "Culture Wars" and "Age of Fracture" of the contemporary US cultural, intellectual, and political landscape and why the field matters in the present moment.