Donna Summer & Barbra Streisand

It really isn't necessary, I'm sure, to trace the biographical information of either of these artists -- only necessary to say that their one-time disco collaboration remains one of the most successful "superstar duets" in pop music history. Period. Enough (really) is Enough, pun intended!!! Of course, others followed -- Michael Jackson & Paul McCartney, Paul McCartney & Stevie Wonder, Elton John & George Michael, and so on.