I am Kyle's self-indulgence

Going chronologically, my next great Sandman moment also comes from the first story arc, Preludes and Nocturnes.

Dream is still recovering the items taken from him during his imprisonment, and he discovers that his ruby is in the possession of Dr. Destiny (or Dee, as Gaiman calls him throughout the story), who has warped its nature so that Dream can't use it anymore. During their inevitable showdown Dee completely absorbs Dream into the ruby. He then decides to crush it in his hands, ending Dream's existence forever. After he destroys the ruby, Dee is left floating in a field of white emptiness:

What a great reveal! (It turns out that by destroying the ruby Dee has merely released Dream, plus whatever of Dream's energy the ruby contained to begin with, leaving him more powerful than he has been in ages)