With literally hundreds to choose from, creating a list of 20 of our favorite duets was a mountainous task. But there ain't no mountain high enough to keep us from doing it. This list is by no means comprehensive, just a mix of tracks — both well-known hits and off-the-beaten-path gems — that we've loved. (And for all you Michael McDonald fans, "Yah Mo B There" just missed the cut.)
—Sarah Rodman, Globe Staff