My church, the local public radio station, CASE (Council for Advancement and Support of Education) and…Rotary!
I always thought of Rotary as the haven of stodgy old businessmen, but I was approached to join, went to a couple of meetings, and joined. I’m female, in my 40s, work in higher ed, and the first time anyone refers to me as stodgy, I’ll commit suicide.
In no particular order:
American Historical Association
Phi Kappa Phi
Phi Alpha Theta
Episcopal Church
The Reel Top 40 Radio Repository
In addition, I am a member of the board of editors of my college’s history journal.
Society For Creative Anachronism
National Botanical Society
Geological Society
National Geographic Society
Cape League Of Adventurers & Wargamers
This lady walked into a bar, and she asked the bartender for a double entendre.
So he gave her one! 
Various choirs
National Trust
Ecclesia Dei Society
New Democratic Party
New Democratic Party Federal Council
New Democratic Party Lesbian, Gay, Bisexual, and Transgender Committee
New Democratic Youth of Canada
New Democratic Party-Quebec Section
New Democratic Party-Quebec Section Executive
New Democratic Party-Quebec Section Board of Directors
New Democratic Party-Quebec Section Lesbian, Gay, Bisexual, Transgender and Transsexual Affirmative Action Commission
Jeunes néo-démocrates du Québec
New Democratic Party Jeanne-Le Ber Riding Association
Conseil des gais et lesbiennes du Québec (Quebec Gay and Lesbian Council)
Project 10 (an LGBTT youth organization)
Head and Hands (a youth social services organization)
POPIR Comité Logement du Sud-Ouest
Esperanto-Societo Kebekia
Ligo de Samseksamantaj Geesperantistoj
Pasporta Servo
At first, I was inclined to say none, but I guess AAA counts - but is it an organization, or just a business that provides various services for a yearly fee?
My wife is a teacher, and is involved in a veritable alphabet soup of orgs.
Joe
I’m a member of WATCH (and was once even an officer), which is an organization for former participants of Quiz Champion (an English quiz show for Korean high school students). Sadly the quiz show is no longer running and the organization has basically fallen apart, but back in the day we did a lot of random stuff (volunteer translating, planting trees on Arbor Day, holding college fairs for high school students, book clubs, etc).
I suppose I’m a member of the Korea University alum here at UChicago, although organization is too grand a term for our humble gathering.
The NDP-QSLGBT&TAAC? Just rolls of the tongue, that does.
That should, of course, be "rolls off the tongue, but “rolls of the tongue” might likely be the result when trying to spit it out. I hope you don’t have to answer the phone there.
The only organization that I am a part of is the American Institute of Architecture Students (AIAS). Other than that I got nothing.
And the SDMB - don’t forget that!
Science Fiction and Fantasy Writers of America. Fairly active (former treasurer and now on their membership committee).
Albacon Committee (runs a years SF con in Albany, NY).
World Fantasy Con 2007 Committee
National Rifle Associaton
B.A.S.S.
Illinois State Rifle Association
SDMB
National Notary Association
Natural Resources Defense Council
American Rights At Work
And I have a library card, does that count for anything? 
SDMB
I used to be in the VFW Ladies Aux. and Am. Legion Auxiliary but I let those lapse. The ex was a psycho. Long story.
Am involved with some local charities.
My kid’s a Police Explorer with a close by department.
I have a Dominick’s AND a Jewel card.
We just say “the NDP-Quebec LGBTT Commission” for short, but I keep threatening to have a fundraising dinner called the NDP-QC LGBTT BBQ.
The American Taekwondo Association.
The Houston Geocaching Society.
Current Membership and Affiliations:
American Motorcyclist Association - Field Rep
American Red Cross (Cleveland) Disaster Services - Team Leader
Fasttrax Road Racing Club - Racer
Western-Eastern Roadracing Association - Racer
Racing Associates Canada Events - Racer
Lapsed Memberships:
National Society of Black Engineers
Does the SDMB count as an organization?
[ul]
[li]The local Episcopal Church (I’m assistant music director)[/li][li]The local amateur radio club[/li][li]BPOE (Past President)[/li][li]TCI (Tall Club International)[/li][/ul]