Molly's Star Trek "defense system"—and Harry keeps referring to them as "Science Molly," "Scottish Molly," "Communications Molly"...
And she remembered to add a Red Shirt Molly to die at at the first sign of trouble.
Even better, when Spock-Molly goes for Molly's mental Self-Destruct Mechanism and Kirk-Molly tries to stop her, Harry remarks that the classic Trekfight music started playing. And later the familiar red alert klaxon is described as sounding like a teenage girl was vocally imitating it.
Also, Harry's reaction upon seeing Molly's Star Trek "defense system. He comments that people are either Star Trek fans or Star Wars fans. Molly tells him basically that that unspoken rule among nerds no longer applies. Harry is playfully dismayed. This event is subverted when even Uriel tells Harry that he prefers Star Wars.
Mort's reaction after Mister interacts with Ghost Harry.
"Oh sure. Professional ectomancer with a national reputation as a medium tells you what's going on, and nobody believes him. But let a stump-tailed furry critter come in and everyone goes all Lifetime"
When Molly looks upon Harry with her Sight, she is shocked and asks how she can know it's him. The surefire, undeniable proof that he really is Harry Dresden?
"You will go to the Dagobah system. There you will learn from Yoda, the Jedi Master who instructed me."
Which only becomes even more Hilarious in Hindsight when we learn who's been teaching Molly while Harry was away.
When Molly is fighting the Fomor servitors, she makes heavy use of illusion magic, including false walls of flame, which they eventually see through. Then Harry joins with Molly, and creates a similar wall of fire. The result is pure Black Comedy.
Uriel is an archangel. It's implied that with a bare amount of effort, he could lay waste to all of Earth. Harry nicknames him Mr. Sunshine.
Becomes a Genius Bonus if you know what Uriel means in Hebrew. It means either "Light of God" or "God is my Light".
Harry notes that he's probably not the first person to lead an army of ghosts into battle. And he's definitely not the first to lead reinforcements through a Way. But he's dead certain he's the first person to lead an army of ghosts into battle through a Way, and having them start the assault by yelling, "BOO!"
The way a mortal servant ends an awkward conversation with Uriel.
And then he hung up. On speakerphone. On a freaking archangel.
That mortal servant? Murphy's dad. Clearly that apple didn't land too far from the tree.
Why it took thirteen books for the Blue Beetle to be referred to as "Herbie's trailer park cousin," I do not know.
Molly's reaction to possession by Harry.
"So. You've been inside of me. I feel like I should be offering you a cigarette."
Doubles as a Tear Jerker when you (and Harry) realize that she's still holding a torch for him, and has been since book eight.
Butters lays in a really quiet dig when Harry and Murphy refuse to ask Marcone for help. For bonus points, he says it while they're in their Marcone-built and -staffed headquarters.
"No going to Marcone for help. Because that would be... unprecedented."
Murphy discussing Molly's gambit to try and keep Chicago safe, specifically her nickname, "The Rag(ged) Lady":
Murphy: If you're going to create a persona you have to think of these things. Do you know how many extra PMS jokes are flying out there now? Molly: (looking serious) I think that just makes it even scarier? Murphy: Yeah I guess it might. Harry: Scares me.
The conversation with Evil Bob about having a "relationship". Just...so very Harry. The best part? Mouthing off to bad guys is so second nature for him, he actually uses the time to realize that he has not become a monster and whip up an escape plan.
Harry's callback to Agatha Hagglethorn's Victorian-era Chicago demesne in the Nevernever back in Grave Peril:
Harry considers having a demesne and asking Bob for suggestions. Then he realises that asking Bob would lead to suggestions like constructs in French Maid costumes 'and would only get more depraved from there'.