The title choice is just beautiful for this book, especially if you look at it on two different levels. Superficially, it's a great name because the "ocean" at the end of the lane refers to Lettie's pond, which plays a large role in our story. Simple, right?
But then if you want to go a bit deeper, the title works because it suggests something extraordinary (a magical ocean that contains a vast wealth of knowledge) just sitting at the end of something pretty mundane (the lane). Its comparable to saying something like the skyscraper in the hall closet—the juxtaposition is a nod to the effects of magical realism that Gaiman uses throughout his story. Pretty sweet.