September 26, 2012
Denny was -- in his own words -- a "strong, virile, horse of a man" (seriously, he said that) with a real lemon of a heart. Izzie fell for him, hard, and put her entire career on the line to get him a new heart -- even though it meant another patient might die.
Her deviance was successful, and he got his new ticker... only to die of a stroke after proposing to her. Ever since then, we'll never hear Snow Patrol's "Chasing Cars" ever again without crying.
(Of course, the impact of his death was lessened by Izzie's crazy cancer ghost sex hallucinations, but we like to pretend that never happened.)