I'm not going to try to give an exhaustive list of clubs since, as far as I know, there is no such thing. There are resources at by the Sky and Telescope, Astronomy, and SkyNews web sites with larger lists. This is merely clubs which are relatively local for me. So, if you are in the New York City area, this will be of interest, otherwise check with one of the above sites.
- Amateur Observers' Society of New York — An active, friendly club which meets in Freeport, NY and observes at Robert Moses State Park both on Long Island.
- Astronomical Society of Long Island — An active club which meets at the New York Institute of Technology and also observes at Robert Moses State Park. I have met with them once for an observing session, which is not really the best time to meet people as I am quite certain that I would never recognize any of the people there (except, of course, for Barlow Bob).
- The Rockland Astronomy Club — Sponsors of the annual Northeast Astronomy Forum (NEAF) and the Summer Star Party. Having been to both events, I can tell you this is both an active and a friendly club.
- The Astronomical League — Okay, so this isn't a local club, but there is still a lot of useful information to supplement whatever you can get through your local club. If you belong to a local club, you may already be a member of the Astronomical League!
- The Astronomical Society of the Pacific — One of the oldest amateur societies with a definite bent toward the semi-professional. They sponsor activities to connect amateurs and professionals with each other and to connect both with educators.