Hi all.
Been playing Scottish and Irish tunes a lot over the years.
The Scottish because .. well I’m Scottish.
The Irish because they often fit beautifully on the flute and are great to play.
Lately picked up Fur Elise, Take Five and the theme tune for Vision On (British Islanders of a certain vintage will recall. Find it on YouTube)
Very refreshing they are to play after a blast o jigs an reels.
Question is…
Can you recommend any others here???
I’d include aires in that too.
Cheers.
You can play just about anything you want, & it doesn’t have to be folk, British, or American, it’s all good, play what you like to hear. 
(I don’t play Irish music! - there you are, I’ve said it. 
)
Serenade to a cuckoo, the Roland Kirk song
https://youtu.be/_q8Ye58uL5o
Curly top, Nicole Mitchell
https://youtu.be/VAWuqSOafLg
A lot of the Gypsy Jazz repertoire would work–here’s a guy playing “coquette”
https://youtu.be/MpKAxZGWN98
A song like “Menillmontant” would be a lot of fun
https://youtu.be/N4zOi8h-Uds
Here’s the commonly used “Django Fakebook”
https://geosci.uchicago.edu/~archer/jazz_band/sheet/fakebook_django_2008.pdf
A wealth of gorgeous American fiddle tunes (Old Time Music),
as in: https://www.youtube.com/watch?v=c0Ul8QCZvng
Also, IMO you can play blues on any instrument that wails.
Irish flute (more gutsy than the typical silver flute) is a blues instrument.
Very easy to play along with this (https://www.youtube.com/watch?v=c0Ul8QCZvng).
One can’t really lead but one can back these people up in interesting and
satisfying ways. Blues.
Hymns and christmas carols sound beautiful on my keyless flute. I’ve also been practicing Greensleeves and Over the Rainbow.
Obviously, there is the classical music of the 19th & 18th centuries, Beethoven, Mozart, Chopin.
Duets and small chamber from the Baroque era, like Telemann.
See Henrik Norblek’s Swedish tunes. Often played in duets with really weird chords. Find a fiddle player to work with:
http://www.norbeck.nu/abc/
Choro music (roots of Samba) often uses flutes. See this great resource:
https://www.choromusic.com
I’m too late in life to fall down another musical rabbit hole, but if I did want to do that it would be Choro. A beautiful mix of South American soul and improvisation.
I’ll echo much of what Jim has said above. Old time/Americana tunes work, 60s folk often works well, and I’ve been playing a ton of blues recently with friends during socially distanced street corner jams out front of my house. Blues just works on Irish flute if you can get the feel for the riffs.
Eric
Grow some mutton chops and rock out bro: https://youtu.be/sB6rpF6W1oQ
https://www.youtube.com/watch?v=06Qm-Z5OsHw. Band I’d like to join.
https://www.youtube.com/watch?v=UcCHRW8G9yY Vision on Theme tune. Left Bank Two. Funny name. Great tune. Needs the low C.
Hope there’s lots more to come.
Thanks peepil.
Hi, here is a suggestion that might be alternate trad. I have been playing a lot of tunes from the Barnes Books. There are 3 of them, blue original, red, and green, the most recent. These are largely for English Country Dance in America, and other places. My wife has gotten into ECD and she likes hearing the tunes 
https://cdss.force.com/commons/s/product/the-barnes-book-of-english-country-dance-tunes-vol-2/01t1M00000LvES8QAN
The tunes have a lot in common with Irish and Scottish origins, and start with the oldest tunes back to the 1650s. There are lots of contra dance tunes and other modern compositions in the more recent collections. The thing I like is that the tunes go through a number of keys besides D and G, forcing me to use some of those other keys on my flute.
Lewis
For English dance tunes, there’s always the Playford tunes. I actually probably spend more time playing them than anything else.
Telemann wrote a set of six Canonic Sonatas that sit very nicely on a flute and stand alone well.