All humour aside, my favourite all time opening paragraph to a novel is in Rebecca by Daphne DeMaurier. "Last night I dreamt I went to Manderley again. We would not talk of Manderley, I would not tell my dream. A cloud, hitherto unseen, came upon the moon, and hovered an instant like a dark hand before a face. Nature had come into her own again and little by little, in her stealthy, insidious way had encroached upon the drive with long, tenacious fingers."
More to topic, for C.S. Lewis, it would be "Once there was a boy named Clarence Eustace Scrubb, and he almost deserved it."