And check out the Revels. Starting in Cambridge, they do Yule and May or Summer Solstice and Sea celebrations with traditional music and dance, Morris dancers, shape note hymns, folk stories, and a whole lot of joy, for going on forty years now. And they're always looking for singers and dancers (it's volunteer). They do group song sessions too. They have organizations in WA, CA, CO, OR, TX, DC, NY, MA, NH. If you're near any of those, check them out (They've done "Brightest and Best" in some of their shows I've seen, gunga)
http://www.revels.org/