Beatam me dicent omnes generationes, quia fecit mihi magna Qui potens est.
All generations shall call me blessed, because He that is mighty hath done great things for me.
Here is the chant proper, in a YouTube video:
Here's an mp3 from the Benedictines of Brazil, and here is the chant score:
Here's a really dramatic piece of Assumption art, from Francesco Botticini and the 15th C.:
I like the "Dormition" theme a lot better, though. This one is from Gherardo Starnina of Florence (c. 1404-1408), and now hangs in the Philadelphia Museum of Art:
And this one is part of the "Grudziądz Polyptych", in the National Museum in Warsaw: