Do you mean with the male having the higher pitch?
A lie was told...
Dat Troper
Yeah. I'm a bit tired right now and I phrase things poorly :P
Apparition in the Woods
Yes, they do, though the only example I can think of right now would be something by Mars from their late period, which is hard to find and probably not what you're looking for anyway...
I'll hide your name inside a word and paint your eyes with false perception.
"My Secret Friend" by I Am X may count, though it's quite close. I've heard from some people who didn't know it was a duet...
edited 8th Mar '12 8:19:10 PM by Daremo
Creed of the Happy Pessimist:Always expect the worst. Then, when it happens, it was only what you expected. All else is a happy surprise.
A chub from the Grant Corporation
Possibly Fleetwood Mac’s “Don’t Stop,” which features lead vocals by Lindsey and Christine?
Confirmed Bachelors: the dramedy hit of 1883!
First one that I thought of was "You're the Reason God Made Oklahoma" by David Frizzell & Shelly West. Not extremely different, but David's voice is still noticeably higher than Shelly's.
https://www.youtube.com/watch?v=pPM7FmLtyPs
(By the by, how does I embedded video?)
Do they exist? I really want them to exist.