Madonna - "Jump"

Arguably Madonna's best dance song since 1990's "Vogue" was "Jump" from her Confessions on a Dancefloor album in 2006.  The song didn't get played by many CHR/Top-40 radio stations, but did climb to #21 on the Hot Adult Contemporary Chart.  Had Madonna waited a couple years for the Timbaland/David Guetta/Calvin Harris era to begin, the song would have been her defining song of the 2000s.

Robert Miles - "Children"

The foundations of the Adult Contemporary format come from instrumentals.  I remember my Grandma working a jigsaw puzzle back in the early-80s and listening to "beautiful music" on FM100.  The station somehow was a ratings juggernaut while playing such songs as "The Theme From Hill Street Blues".  Fast forward to 1996, and pop radio was playing "Children", an instrumental from Italian DJ Robert Miles--think of him as 1996's Calvin Harris or Avicci.