The Annunciation and Two Saints [St. Ansanus & St. Maxima/Margaret], Simone Martini (1333)
cf. Lk 1:26-38
For more about this remarkable painting, check out this quick video from Khan Academy. With each passing season, I am always progressively amazed and delighted with some previously undiscovered-by-me piece of sacred art.
If you're looking to work through the Jesse Tree this year, check out this great set of printable ornaments. I always struggle each year to find a quality set of ornaments that aren't preschool-grade felt cutouts, and I love that these feature fine art.
Check out Busted Halo for a fun alternative Advent Calendar.
Finally, if you haven't already read the third part of Pope Benedict's Jesus of Nazareth, Advent is a great time to pick up The Infancy Narratives. It's a short little book, but packs a good punch for Advent prayer and reflection.