sacred harp
Holly and I are attending our first ever sacred harp sing this Sunday, in Manhattan.
fasola.org
http://www.manhattansing.org/
I've wanted to do this for about two years, but michigan didn't have a group and new york has several--2 in manhattan, and one in brooklyn.
If you've never heard sacred harp singing, check out the fasola site---they have a good amount of recordings.