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. Thanks to everyone for all 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 it I stayed up a bit too late a number of times.
Worth it.
I normally go for parodies, but this would be the place to post the Devil Went Down to Georgia (Washing Machine Cover)
More seriously, 2CELLOS’ rendition of Thunderstruck is incredible: https://www.youtube.com/watch?v=uT3SBzmDxGk
They have a ton of really good ones on their channel, but that one will always be my favorite for how into it they get