Bluegrass is probably not in “popular music” but the group IIIrd Tyme Out used to do a lot of acapella stuff (members have changed - don’t know about now). This version of “Only You” is a good example:
I’m listening to Pink Floyd’s *Animals *album this morning, and it reminded me of the harmonies in The Show Must Go On from The Wall; they’re present throughout the very short song, but especially strong in its final seconds before the segue into In the Flesh.