6. Usher & Alicia Keys "My Boo" (2004)
Producer: Jermaine Dupri
Back in 2004, there were no hotter R&B artists than Alicia Keys and Usher. The two had connected previously on the remix of Keys' highly-sucessful 2004 single, "If I Ain't Got You," and Usher was dominating the charts with smash hit after smash hit from his Confessions album.
This time, the duo linked up with "My Boo." Usher sings about his view of a past relationship and how feelings are still there for one another. Keys agrees: "Even though there's another man who's in my life/You will always be my boo." Years later, the single will go down as one of the best duets of all time.