right - I realise that only "a" song opening was requested, but there's so many cajillions of them - I'll make these the last ones:
"Hello darkness my old friend....." - S + G
"Out here in the fields......" - The Who (Baba O'Reilly)
"Imagine me and you, I do......I think about you day and night, it's only right." - The Turtles (Happy Together)
"Didn't I make you feeeeel........Like yooooooouuuu were the ooooon-ly maaa-aa-aaaaan?" Janis Joplin (Take Another Little Piece of My Heart)
edit (I KNEW there was one I was forgetting):
(from the saddest all-time song): "It's a god-awful small affair, to the girl with the mousy hair" - David Bowie (Life on Mars)