This was on another music thread and I loved it (and was the main reason for this thread)
This thread is for songs where the singers are not a traditional duet. Examples of traditional duets could include Simon and Garfunkel, Jan and Dean, the Judds, the Carpenters, et al so songs by these artists should be excluded.
I'll start with Meat Loaf and Cher
Run DMC ft. Aerosmith