Harry's final conversation with Lasciel, where he makes her realize that she does have a choice and that she can redeem herself. And then, in the final confrontation, she accepts the psychic backlash from escaping the mind-control spell, effectively sacrificing her existence for the sake of Harry's. Redemption is, indeed, a beautiful thing.
Minor clarification: It wasn't Lasciel the Fallen, but Lash, the "shadow" living in Harry's head. Harry actually gave her a portion of his soul, and her sense of self in the process, which just makes it more heartwarming.
The final conversation of the book between Ramirez and Harry, with Ramirez saying he's with Harry 100%, especially when Harry watches over him sleeping the whole night because "you don't leave an injured friend alone."
Molly, terrified and more than a little scarred, finally learns why Harry fights, and still steps forward to fight as well. Her father's daughter, indeed.
Glimpses of Marcone's inner good nature always end up being CMoHs. The best is in here, when Marcone is providing an extraction route for Harry and the battle gets heated. Marcone tells Harry he didn't sign on for a war. Harry responds by going up to him and saying:
"People are dying, John. Help me save them. God, please, help me."
"Who do you think I am, wizard?"
"Someone who can help them. Maybe the only one."
He stared at me with empty, opaque eyes. Then he said very quietly, "Yes."