The Statler Brothers sang a little country and a lot of gospel. They were backup singers for Johnny Cash. I've always viewed them as the barbershop quarter of country music.
The Class of '57 is the song I feel highlights their vocal ranges the best while still being whimsical.
httpv://www.youtube.com/watch?v=EAWOgXMeldU
And, of course, you can't listen to The Statler Brothers without spinning this record.
httpv://www.youtube.com/watch?v=fbk8uiuJimE