Today's earworm: Gold.

Specifically, "The Ecstacy Of Gold."

Originally I heard it in The Good, The Bad, And The Ugly, but later heard Metallica's cover of it. (This struck me as amusing in a similar manner as when I heard their cover of "Whisky In The Jar.")

Just now, while looking to hear it, I found this live version of Ennio Morrione directing a full orchestra and choir to perform it in its most traditional manner.