Professional organizations, in all their variety, are important resources for research, teaching, study aids, scholarship and fellowship opportunities, blog sites — you name it.
The two most important organizations for classicists in the United States are:
Two organizations with valuable resources for undergraduates:
Regional Classics Associations in the US:
Classical Association of New England (CANE)
CAAS (Classical Association of the Atlantic States)
CAMWS (Classical Association of the Midwest and South)
California Classical Association Northern Section
Williams is an institutional member of:
Also of interest:
Lambda Classical Caucus, a coalition of queer (broadly construed) classicists and their friends and supporters, with a political and scholarly mission. Lambda is affiliated with the American Philological Association, but its membership is open to all. It publishes Iris.