A line by John Gregory Dunne, chosen by author S. J. Rozan as his favorite opening line ever written. The Atlantic has a list, including choices by Margaret Atwood and Jonathan Franzen.
Most of them don't impress me much, though I like that one, and the Hemingway. But I guess that the success of a first line is tied pretty closely to what comes after. Mine is the opening line of The Good Soldier: "This is the saddest story I've ever heard." But if you haven't read the book, you can't fully grasp the sad irony of that line, can you?
What about you guys? What's your favorite opening line?