The AEA is by far the largest professional organization of economists in North America. It is an umbrella organization including members of all specialties and perspectives. Anyone can join and basic dues are low. Membership includes online access to eight economics journals published by the AEA. More can be found by visiting AEA.
Every January, the AEA and a number of smaller organizations sponsor joint four-day meetings in a major U.S. city. The meetings consist mostly of seminar sessions in which economists present their research. The formal name for these meetings is the "Allied Social Science Associations," but they include only economists.
The AEA also hosts Job Openings for Economists, a website for jobs in economics. Some of the nonacademic job openings listed do not require an advanced degree.
NABE is an association of economists working in the private sector. Its members are mostly concerned with forecasting and the effects of government policies. Chapters in major cities sponsor regular meetings and speakers. Many of its members have BA, MA, or MBA degrees, rather than PhD degrees.
The MEA's members mostly teach at colleges and universities in the Midwest. The MEA sponsors a three-day conference every March, often in Chicago. The meetings consist mostly of seminar sessions in which economists present their research.
ES is truly an international organization, including economist members from every continent except Antarctica. Its focus is on "the advancement of economic theory in its relation to statistics and mathematics." Its members are mostly economic theorists or econometricians. ES publishes Econometrica, a prestigious but very technical journal.
ES sponsors annual meetings on each continent and world meetings every few years. North American meetings are held twice a year--once in January jointly with the AEA and once in the summer at a major university.
There are many other organizations of economists. Most focus on a particular subfield, such as labor economics, or serve a particular region, such as the South.
Most organizations offer discount memberships for students. To get the discount, often you must submit a copy of your student ID card. Most organizations give the student discount only for a limited number of years.