I think this warrants its own thread.
One I was thinking about just now:
The Turtles, "Sowing the Seeds of Love"
Others I've imagined in the past:
Franz Ferdinand, "Nineteen Hundred and Eighty-Five" (Wings)
Nina Simone, "Feel Like Makin' Love" (Roberta Flack, you ninnies)
The Strokes, "No Good to Cry" (Wildweeds)
George Michael and Andy Bell duet, "Windmills of Your Mind" (Dusty)
Tracy Chapman, "If You Could Only See" (Tonic)
Booker T. & the M.G.'s, "Indian Reservation" (Don Fardon / Raiders)
Natalie Merchant, "Road to Nowhere" (Talking Heads)
Fred Schneider, well, anything, but especially
Fred Schneider, "Wild Wild Life" (Talking Heads)
Polyphonic Spree, "Porpoise Song" (Monkees)
Big & Rich, "Let Your Love Flow" (Bellamy Brothers)
Big & Rich with Cowboy Troy,- "M'Lady" (Sly & the Family Stone)
Evanescence, "Woman in Love" (Barbra Streisand)
Gretchen Wilson, "Lawman" (Jefferson Airplane)
Let's hear 'em.