Joining up

Currently I belong to exactly zero gardening related clubs, societies, or associations. When I was a teenager going through my rose phase, I belonged to The Rose Hybridizers Assocation, but since I've (mostly) grown out of roses, I've not been a part of such organizations. I did, once, attend a meeting of the Michigan Orchid Society, since I have never had, and never plan to have, an orchid phase, and I only attended under the coercion of a friend, I didn't join.

So I belong to nothing. And yet, there are all these gardening organizations out there, presumably full of cool, plant-obsessed people. People I could learn stuff from, share plants with, all of that sort of thing. So I'm thinking about joining up. Based solely on the recommendation of the good people at Arrowhead Alpines, I'm considering joining the North American Rock Garden Society (NARGS) and its local Great Lakes chapter. I'm not a rock gardener, but apparently these people are mostly just all-around unusual plant nuts, and membership in the national organization gives one access to an apparently amazing seed exchange, and the local chapter has members-only, kick-ass plant sales.

That all sounds pretty darn cool. And makes me wonder what other cool organizations are out there, that I don't know about? Do any of you belong to great gardening organizations? Which ones, and why do you like them?