How Can Love Survive from the Sound of Music. Bear with me on this. While this is kind of a love song, the two characters are not actually the ones in love.
All the duets between Ziggy and the Robot Waiter on Starmania. The originals are in French, but there's an English translation by Tim Rice called Tycoon. I'm not familiar with the translation, but from the original "La chanson de Ziggy", "Nos planetes se separent", "Duo d'adieu". Admitedly, their respective solos are more interesting.
Avenue Q - Fantasies Come True - Kate and Rod Boy from Oz - You and Me - Liza and Peter Kiss of the Spider Woman - A Visit - Aurora and Molina Taboo - Sexual Confusion - Philip and Sue Don't You Wish? - Zanna Don't - Roberta and Mike
EDIT - Missed the part about comedic. Only the Taboo one really counts there.