Probably my favourite contemporary piece by a non-accordionist composer (who wrote for accordion) is the Intermezzo for violoncello and accordion by Isang Yun. The piece blends light and shade, harmony with dischord, overlapping textures and the tones of string and reed are marvellous. You can almost hear exotic birds singing at times. It's a very organic sound to my ear. I've listened to this piece so many times and I discover new details every time.
I get that the Contemporary era can seem like a strange musical jungle for accordionists, an environment where the everyday rules of music no longer apply. Having completed two short contemporary composition courses with Cardiff University, I'm beginning to understand it a little better. For example, it's perfectly standard in contemporary composition to have absolutely no key signature and the 12 tone technique gives no importance to any note, a significant departure from tonal music. Yet the 20th and 21st century are far from being the only times when the music styles can seems vastly different to the popular music of today.
Let's jump back 500 years to the Renaissance period. This was a time before tonalism - the framework where tunes are set in the major and minor keys. However, back in the Renaissance and for vastly the longest time in music history, back to the early medieval times, it was actually the modes (and not tonality) that formed the framework for music. Tonality and atonality are very much the newcomers in the grand scheme of things.
So, to get us started, when I think of Renaissance music played on accordion a name that comes to mind is Josquin de Prez (c. 1450-1455 to 1521). Here we can listen to two little bicinium (two part works) in different modes played by the Italian accordionist Ivano Paterno.
Bicinium - Hypomixolydian (mode VIII)
Bicinium - Phrigian (mode III)
Also, I cannot look past the work of Antonio de Cabezón. His piece Diferencias sobre el canto llano del caballero is beautiful. Miss Vicens plays it well...