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
STRFKR - Girls Just Want To Have Fun, synthy goodness
Kishi Bashi - This Must Be the Place - more orchestral version of the Talking Heads song
Gorillaz - Crystalized - somber cover of the XX song
Placebo - Running Up That Hill - Running Up That Hill but… a Placebo song. Exactly what it says on the tin