Here are a few to get things started:
Don Henley’s The Boys of Summer as an 80s synth tune
Bossa nova version of Crowded House’s Don’t Dream It’s Over
Reggae-ish version of Aretha Franklin’s Respect
A capella men’s ensemble version of Lady Gaga’s Bad Romance
EDIT: This has been great, everyone. Thank you all for the terrific links and for introducing me to a number of artists I wouldn’t have heard of otherwise. Seriously, the online rabbit-holes have been thoroughly enjoyable–even if I stayed up a bit too late a number of times.
Worth it.
Postmodern Jukebox ft. Haley Reinhart - Creep (original by Radiohead), jazz/big band style
Novena - Bury a Friend, progressive metal Billie Eilish. Starts out like the original and gets progressively heavier.
Surprised how far down I had to look for Postmodern Jukebox to show up!
Time, the Valuator covered Lovely as well. Pretty fucking amazing.
So many of the Postmodern Jukebox covers are fantastic.