To the alchemists, they are Mercury and Sulphur, to the Regency Era, they are Elizabeth Bennet and Mr. Darcy, and to a lot of people today, they are Ron and Hermione.
Here is what I LOVE about this sort of couple. They not only find true love and live happily ever after, they also have...CHEMISTRY! And lots and lots of sexual tension. Ooooh! It takes an entire movie's worth of fighting and veiled flirting to get to the big kiss at the end.