The Dragon of Wantley has been a family favorite for three generations. My grandmother was given a copy for Christmas of 1902, and it has been read and re-read ever since. My father, who inherited his mother's copy, literally wore the covers off some time in the 1970's (Lippincott was not known for the quality of their bindings), and so our copy was held together with ribbons.
A lesser-known work by Owen Wister, author of "The Virginian", it is a comic tale of the Middle Ages, but one shot through with witty little anachononisms. The story is set at Christmastime in the early 13th century, and involves young lovers, dragons, knights and a rather mysterious abbey of monks. The illustrations are especially delightful, and filled with wonderful details that reward the careful observer.
My one recommendation would be this: if at all possible, find one of the later editions. The author has fun with some of the reviews of his work in his Foreward, and each edition got more of Wister's little asides.
The Dragon of Wantley, along with A Christmas Carol, is mandatory December reading in my household.