First: Carry On, Mr. Bowditch by Jean Lee Latham (first published in 1955). This is a biographical novel about the amazing Nathaniel Bowditch--indentured servant, sailor, navigator and mathematical genius who lived during the turbulent years of America's founding. It is absolutely inspirational.
Next we have When Marnie Was There by Joan G. Robinson (first published in 1967). Initially, I pegged it as a conventional ghost story. But because it is so beautifully written, I continued to read--and discovered it to be far more than I thought. One of the most original and happy stories I've ever read.
Tom's Midnight Garden by Philippa Pearce (first published in 1958) is in much the same vein as Marnie. Despite the terrible title, I was never tempted to put it down. You're thinking it must be a ghost story until the main characters start arguing about which one of them is a ghost. The ending is too beautiful to guess, though the author drops important clues throughout. A better title for this little masterpiece would be something like A Time Travel Mystery or The Timelessness of Intergenerational Love. . . . Okay, I see the problem that the publisher had with compacting the story into a title.
Finally, there's The Thief Lord by Cornelia Funke. Published in 2000, this book came out after I had been published myself, which is no excuse for my not having read it. It's one of those books that you never want to end, which is a crazy thought coming from someone who won't wade through long books. Endearing, unpredictable, magical, uplifting--any cliché you want to use in praise of it works.
So, these are my recommendations. I hope that a few lucky readers on your Christmas list find them under the tree.