Duets. Yes there are literally thousands, though I think the genre (if that's the right word for it) tends to produce more dross than diamonds.

This one is the first to come to mind, for some reason. Probably the pop duet I've heard the most in my life, and yet still enjoy.

Mind you, this one occupies a hallowed spot in the BD pantheon. Amazing song. And nice video too, which I only came acorss now.

Next, any duet discussion would be imcomplete without this archetypal duet from the sixties. Not as laughably crap as their rep, imo. Not their most fanous song, but the one I like the best.

And finally, speaking of archetypal sixties duets, how about this one.