Its Like That & We Belong Together
That's The Way Love Goes & If.
Doesn't Really Matter & All For You (Yeah I'm biased towards Janet lol)
Rolling In The Deep & Someone Like You
Womanizer & Circus
Dangerously in Love - Crazy in Love & Baby Boy Daydream - Fantasy & One Sweet Day (probably more weeks @ #1 than any of the choices in the poll).
Voted 21 - RITD/SLY as that's probably the most successful/iconic duo in the OP
and Loud - WMN/OGITW as those are, qualitatively, my favorite pair in the OP