I know that recently, artists have been releasing two songs at a time (i.e. Beyonce - Single Ladies/If I Were A Boy), but I don't remember anybody else doing it on such a consistent level aside from Toni. Perhaps she is the trailblazer of that as well? She's had 6 in the U.S.!
You Mean The World To Me / Seven Whole Days (Live)
How Many Ways / I Belong To You (In addition, I Belong To You was also released as a maxi single)
You're Makin' Me High / Let It Flow
I Don't Want To / I Love Me Some Him,
Just Be A Man About It / Spanish Guitar (DVD single - which was the official format version of the U.S. single release of these two songs)
Make My Heart /Hands Tied
And here's some interesting trivia. There were some vinyl singles pressed up of another planned double single - Let Me Show You The Way (Out) / Give It Back, but very limited. There are a few copies for sale that sometimes pop up on Amazon and eBay and they were official promo releases.