In reply to Janyoncé Turner.

Nice!

I can think up several collaborations for albums or singles from different artists that would either worked at one time (or even now). Those would be:

Beyonce & Christina
Beyonce & Adele
Rihanna & Pink
Janet & Aaliyah
Janet & JLO (definitely 10 years ago)
Janet and Madonna (would shock now)
Brandy & Alicia (Bran and Mo already came together)
Mary & Monica
Maxwell & D'Angelo
MJ & Prince
Whitney, Celine & Mariah (song) ... It would have been THE vocal reference to refer to for centuries)
Toni & Sade
Usher & JT (weird, but musically it works)
Ne-Yo & John Legend
Fanny & JHud
Erykah & Jill