One of my favorite depictions of the Dormition is at the base of apse of the Patriarchal Basilica of Santa Maria Maggiore in Rome. Here's a picture from the Vatican website of the whole apse ... look towards the bottom of the mosaics of the Dormition.
An informative write-up at Catholic Exchange.
As expected, Mike Aquilina has juicy reading lined up at the Way of the Fathers, including a link to a piece exploring the foreshadowings of the dogma in Jewish writings.
And, Pontifications has a beautiful quote by St. Bernard of Clairvaux.
::UPDATE:: Definitely check out the photograph of Pope Pius XII defining the Dogma on All Saints Day, 1950, over at Don Jim's blog.
And I absolutely love this motet, set to gorgeous polyphony by Palestrina, for this Feast:
Assumpta est Maria in caelum;
laudantes benedicunt Dominum.
Gaudete et exsultate
omnes recti corde.
Quia hodie Maria Virgo
cum Christo regnat in aeternum.
Quae est ista
quae progreditur quasi aurora consurgens,
pulchra ut luna, electa ut sol,
terribilis ut castrorum acies ordinata?