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.
Me First and the Gimme Gimmes cover of All My Loving
Or this revision of Pioneer to the Falls by Interpol, made by the band’s former bassist Carlos Dengler
https://youtu.be/uq7gEq9Pwws
Their version of Straight Up is genuinely one of the best things I’ve ever heard.
As for their cover of Goodbye Earl, the only criticism I have is that it’s too damn short.
I love the Gimmes immensely, and am disappointed that I had to scroll down so far to find any mention of them. Their guitarist is in one of the world’s biggest bands ffs!