With the roses entwined together
On the river bank covered with flowers laughing in the morning
Let us descend together!
~The Flower Duet
Today, the Flower Duet from Lakmé by Leo Delibes. As NPR notes, "Even people who say they never listen to classical music most likely encounter it nearly every day... [and] there may be no classical tune — operatic or otherwise — that turns up in more varied places than [The Flower Duet]."
This song has been used in everything from The Simpsons to Sex and the City. The video below doesn't say, but I think the singers are Dame Joan Sutherland and Jane Berbie.
Another version, featuring sisters: