This is a tough one - but I am going to go with the "Apparition of the Virgin to St. Bernard" that hangs in the Badia Fiorentina.
I have written about this before (check the link or click on the image). I will add as runner ups Pontormo's Deposition (also mentioned here) and Perugino's Crucifixon. If you have the time, leave the beaten path for a moment to check out these masterpieces - you will be glad you did.
