Three local (Lancashire, UK) trios:

Hands in Pockets, wonderful unaccompanied harmony material, and established for a good number of years (can't remember how many).

Wench All, another unaccompanied harmony group, first saw these a couple of years ago.

And an even newer trio, the Saggy Bottom Girls, who use various instruments as well as singing unaccompanied harmony.

All three groups are getting regular gigs in the north-west, and are worth seeing.

And a local female duo who deserve to be better known: Bailey's Boot. Again, if you see the name advertised, do go and see them, you won't be disappointed.

Joan