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
Oh I absolutely love covers. My favorite weird cover is probably Tiny Tim’s cover of The Doors song People Are Strange https://youtu.be/kzoH88GFqK0