''Take my camel, dear,'' said my Aunt Dot, as she climbed down from this animal on her return from High Mass.
Maybe it's just the company I keep but favorite opening sentences come up every now and then but this has to be my all-time favorite. It's from Rose Macaulay's 1956 Towers of Trebizond and the rest of the book--one of those quasi-satirical, quasi-despairing looks at eccentric Brits on the edge of a crumbling empire--is nearly as good. It's the only thing of hers that I've read but have sometimes been tempted by a historical novel set in the 17th century that uses only a vocabulary positively known to have existed at the time. I believe this is They Were Defeated but can't confirm it right now and hope that I didn't imagine this whole thing.
And while on the topic I don't know where else I will ever get a chance to mention that when I wrote a piece on Godzilla for Joe Bob Briggs' long-gone Monstervision website I used the opening sentence for Remembrance of Things Past though completely unacknowledged of course.
There's a variation on openings to SF novels at http://io9.com/5027128/great-opening-sentences-from-science-fiction though it seems a bit narrow to me. Still, the opening to Neuromancer is certainly a great one and almost entirely because of one omitted word: "the color of television" with no definite article for "television".