I love the opening line from "Pride and Prejudice."

The opening line of "Northanger Abbey" is also really good too: "No one who had ever seen Catherine Morland in her
infancy would have supposed her born to be an heroine." (Jane Austen)

I have three or four favorites, but couldn't possibly put them in any definitive order. The ones that catch my attention right off are:

Phillip Wylie "When Worlds Collide", "The Secret itself was still safe." Now that's a short hook.

Vincent Bugliosi "Helter Skelter", "It was so quiet, one of the killers would later say, you could almost hear the sound of ice rattling in cocktail shakers in the homes way down the canyon." Still sends chills up my spine.

Margaret Mitchell "Gone With The Wind" "Scarlett O'Hara was not beautiful, but men seldom realized it when caught by her charm as the Tarleton twins were." The first romance with a heroine who didn't look like Miss Universe.

Christopher Moore "The Stupidest Angel" Christmas crept in to Pine Cove like a creeping Christmas thing: dragging garland, ribbon and sleigh bells, oozing eggnog, reeking of pine, and threatening festive doom like a cold sore under the mistletoe." My sentiments, exactly.

Like that I have many but one that particularly stands out has got to be

Terry Pratchett "Reaper Man"

"The Morris dance is common to all inhabited worlds in the multiverse"

Gotta love it

Charles Dickens´from !"A Tale of Two Cities" :" It was the best of times. It was the worst of times."
This opening sentence applies to every time in Man´s Histoty.

"Last night I dreamt I went to Manderlay again."
From 'Rebecca', by Daphne du Maurier.
or
"In a hole, in the ground, there lived a hobbit."
From 'The Hobbit' by J.R.R. Tolkien.