In know it couldn't be any less than two [!], but this is a quick post to refer to four examples of male and female [that's just how it is] dual harmony that I have particularly enjoyed this year:
Gillian Welch and Dave Rawlings, with no more needed to what has been said already.
The Civil Wars - Joy Williams and John Paul White. It wasn't till seeing them on Later...with Jools and hearing a bootleg recording of a concert performed this year that I realised how superb they are and returned to their album Barton Hollow, though it's live where they excel with just acoustic guitar and vocals.
Pharis and Jason Romero, who are even more ethnic in their Country than Welch and Rawlings, but harmonies just as tight.
Tiny Home - Sonya Cotton and Gabe Dominquez - who sing beautiful tight harmonies, and advertise online to perform at weddings and functions in the San Franscico Bay area in ecologically considered contexts. They do a superb version of Van Zandt's If I Needed You.