Which professional societies to join?

As I transition from my current job to my startup, I've started to think about my professional society memberships.  Overall they have been useful in personal and professional networking with other professionals in my field, presenting technical publications, and receiving member discounts.  I plan on maintaining membership in most of them, but some will be less useful as I move into my new line of work.

The one professional membership that I've maintained since my freshman year in college has been the American Institute of Aeronautics and Astronautics (AIAA).  It is the world's leading society for aerospace professionals, and it has proven to be value for my money through its journal publications, its trade magazine, and the interaction with members at the local chapters.  Mathematics aside, there's very little overlap between the aerospace and sport statistical analysis spheres, but aerospace engineering has been a big part of my life for so long that I will more than likely maintain my membership.  I've been active in AIAA at various levels and I am in the process of becoming a life member, so I would like to remain involved in that community when I move to Atlanta.

I'm also a member of the Institute of Electrical and Electronic Engineers (IEEE), which is the world's largest professional society (I think).  I think of IEEE as an umbrella organization with an extremely large number of societies, such as Computers, Aerospace Electronics, Medical Electronics, Nuclear Physics, and other areas of the hard and soft sciences.  I became a member of the IEEE Control Systems Society since 1998, but not a very active one — I feel like I need a Math PhD just to be able to understand their control systems journals!  If I had to choose, I would let this membership slide.

I used to be a member of the Society of Industrial and Applied Mathematics (SIAM), whose name is a very accurate description of their interests.  They have excellent books on numerical methods which are worth the price of the membership.  I've never been to their conferences, however, and their journals are just as intimidating as some of the IEEE ones.  I would still maintain this membership in my new career because of the resources they have to offer on statistical and numerical analysis. 

One society that I am not a member of, but might join in the future, is the American Statistical Association.  Like a lot of other societies, it has a large number of sections and specialty groups, but the Statistics in Sports and Bayesian Statistical Science sections would be most relevant to me.  However, I am not sure whether membership would be of much use to me; perhaps some readers who are ASA members could weigh in on that subject.

Of course, the way to find a professional society that meets your needs is to form your own.  Several people have asked me if there exists a society for soccer stat analysis, similar to SABR or APBR, and the answer to that is no.  I joked half-seriously that the first thing to do was think of a clever name who acronym sounded like "soccer", but the best I could come up with was SOFA/SOSA (Society of Football Analysts, or Society of Soccer Analysts).  I think that the objectives and benefits of the society could be agreed upon it would become very popular, but it seems that no one wants to do the heavy lifting and organize it.  I would be willing to do the heavy lifting, but I have too much going on (moving, completing projects, launching the startup).

MORE: I forgot about INFORMS, which is the Institute of Operations Research and the Management Sciences.  A number of problems that I'm investigating fall within the general area of operations research and analytics, so INFORMS would be ideal.  They also have a section on operations research in sports called, well, SpORts

Thanks to Matt in the comments for bringing that organization to my attention.