The Louvin Brothers were one of the very best country duets. Gram taught Emmylou about them & she carried it on…
There’s a tribute album called “Livin, Lovin, Losin”…
(And there’s Emmylou’s Duets–compiled from various projects.)
I’m going to be really esoteric here, and recommend a duo that may not have played together since the 70s, but I remember liking them quite a bit on the record I heard (yes, it was vinyl): Wendling and Hansen. Google didn’t turn up much, but maybe some other posters here remember.
I won’t echo the great suggestions in this thread, some of which are treasured in my playlist, but how about Ralph Stanley and Patty Loveless singing Pretty Polly? Ralph Stanley and Patty Loveless - Pretty Polly - YouTube
Wow - that was cool. Thank you for sharing that.
I can offer Dwight Yoakam and Ralph Stanley - Bluegrass Duet
it is on
The Doc Watson Family SFW40012
1990
Smithsonian Folkways Recordings
Doc always sings well with other people.
I like Darius Rucker and Nancy Griffith on Gulf Coast Highway.
And to expand on what Gary T said, I think pretty much anything by Ian & Sylvia qualifies as a “great folk duo” 
Can someone please correct me, as these are not my native styles…
But I thought Bluegrass != Country != Folk. Lotsa crossover stuff, but not the same thing. No? Thanks.
Those lines are not that bright. For example, John Prine, the guy named in the OP, is kind of hard to categorize. He’s not exactly bluegrass, not exactly folk, and not exactly country. Same goes for Iris Dement. These days folks are using the label “Americana” to try to embrace a broader range of styles, and I think most of the acts mentioned in this thread would fit that category.
Hey, speaking of Iris Dement, here’s my favorite tune of hers: Let the Mystery Be
Well, there are marketing categories & those used to program the more programmed radio stations. Then there is reality…
Bluegrass is a style devised by Bill Monroe, adding bluesy improvisation to Old-Time Music. Except that Old-Time Music was already a mixture of songs & fiddle tunes from the British Isles & African-American String Band music; the banjo has African roots.
Country Music is the larger genre–originally called Hillbilly music by the record companies; it includes Honky Tonk, Western Swing & Bluegrass, although most of what’s heard on mainstream Country radio is more like soft rock. Then there’s Alt.Country–an attempt to Get Back To The Roots.
Folk could be the indigenous music of any culture around the world. In the USA it often means music inspired by field recordings & ancient records (see Old-Time & String Band–also The Blues), growing in popularity among the “young folks” in the 50’s & 60’s. Some of them set their own words to old tunes & a few even wrote new tunes. Then the Beatles hit & many of the folkies turned on & invented Folk Rock–or electrified White Boy (& Girl) Blues. Some stayed acoustic. The Singer-Songwriters kept at it, too. (Oh, and the UK had/has its own Folk Rock–& Singer-Songwriters.)
I’m tempted to say “fuck categories”–which sounds rude–but that’s just what keeps happening. The genres continue to go out in the alleys behind the cafes or low dives & conceive new hybrids. (Rock & Roll was one of them!)
Lots of good names have been mentioned in this thread. Check them out–Youtube is good. Also recommended: Watch O Brother Where Art Thou. Find the original tunes & artists “covered” in the movie; find out what else the performers have done…
And speaking of John Prine and duets and bluegrass, here are Jim and Jesse doing a bluegrass cover of what may be Prine’s best-known song: Paradise.
Also Down From the Mountain.
Goes along with O Brother Where Art Thou.
One my faves is the unlikely collaboration of Ismael Lo and Marianne Fathfull singing a song from Lo’s Jammu Africa called Without Blame sung in french and english - it’s beautiful.
My non-standard view is that these genres are descriptions of styles that at best apply to songs.
John Prine is not bluegrass, he might have done a song in the bluegrass style but I’ve never heard it.
More generally a person isn’t a genre, they might perform on occasion a song in a genre. They might exclusively perform in the genre.
Partly marketing but at the heart, genres are about songs in a similar style. Performers who work in multiple styles are my favorites but hard to find in the CD section of a store.
In the bluegrass genre if you like the harmony vocals look for Third Tyme Out, Doyle Lawson or Blue Highway.
If you like the “High Lonesome” sound, look for Bill Monroes’s work or for a current band doing that style listen to Del McCroury.
If you want songs from other genres arranged in the bluegrass style, look for Country Gentlemen or the Seldom Scene.
None of those are exhaustive lists, just starting points. Also, many of those groups performed for years with regular changes to their lineup. This can also help if you get into it very deep. My favorite Country Gentlemen line up was the mid-70s one that recorded the album “Joe’s Last Train”. It included Doyle Lawson who later formed his own band and Third Tyme Out" was formed by two members of Doyle’s band.
One fine duet that’s also an example of mixed genres: I’m Still in Love With You. Steve Earle & Iris Dement, from Steve’s The Mountain–with backing by the stone* bluegrass Del McCoury Band. Steve came out of the Texas folk/singer-songwriter scene, has voiced his strong political beliefs & has played in every style from hard rock to honky tonk toIrish.
- Stone: Hard Core Traditional. Not “Stoned”–which Steve has been in the past. He was one of the many who sat at the feet of Townes van Zandt & thought that emulating his weaknesses would make him a great songwriter. Steve survived & learned better…
If you have not heard to glory that is Dick & Mimi Farina, check them out now..
The is the link for del Gato:
The album was entitled “So Rebellious A Lover”. You know Gene from the Byrds, of course, and if you don’t know Carla I strongly recommend the Textones’ “Through The Canyon”. “Cedar Creek”, not so much.
The last computer upgrade at work seems to have disabled You Tube audio, so I assume the link works even though I can’t hear it…
OLD FOLK MUSIC
Bob Gibson and Hamilton Camp - many albums, classic harmony singing
1980’s BLUEGRASS and COUNTRY Ricky Skaggs and Tony Rice,
George Jones and Johnny Paycheck
NEW BLUEGRASS Chris Thile and Michael Daves - This is one of 6 2011 albums nominated for GRAMMY Best Bluegrass Album
Enjoy
David
Where is John Belushi when you need him?
Kidding, kidding.
Well, sort of.
How do you feel about instrumentals?