This exchange when Thomas admits to calling his sister and threatening her for information.
Harry: So you're telling me that I just engaged in blackmail against the ruler of the White Court. By proxy. Thomas: Yeah. You've got some great big brass balls on you to do something like that, Harry.
Doubling with the book's Crowning Moment Of Awesome, Sue, the zombie T-Rex, stomping through Chicago. Particularly the reactions from the people who see her coming—the military, the Wardens, and the villains. Then there's when Dresden reminds Butters to keep the beat going.
Butters: I know, I stop playing, no more dinosaur. Dresden: No, you stop playing, dinosaur does whatever the hell it wants.
Another one right afterward:
Butters: My God, you're like a living wrecking ball! ....hey, can we swing by my boss' house? He won't shut up about his new Jaguar.
Harry: Maybe later.
And it even helps Harry make friends:
Warden Ramirez: Everyone else who lets me ride their dinosaur calls me Carlos.
And later on, a funny-as-hell moment by implication. Said dinosaur was controlled by Butters' polka suit, right? Well, while Harry's off saving the day, Butters attends to Warden Luccio's wounds, and while he's doing that, Morgan takes over drumming for him. Just the image of stern, serious Morgan operating a one-man polka suit is hilarious.
Except Morgan couldn't have worn the suit. The reason he stayed behind was because his knee was shattered when Ramirez shot him to keep him from killing Harry, and the drum portion was used by kicking or marching. Most likely he kept the beat simply by using the drum like a normal one. Granted even that image is pretty funny.
"Because I'm too stubborn to die. And Thomas is too pretty to die. And you aren't going to die, Butters, because tomorrow is Oktoberfest and polka will never die!"
Which turns into a Running Gag in Changes, when Harry once again reminds Butters that polka will never die.
A tiny, almost unnoticeable FridgeJoke that manifests in book Cold Days. Bob makes a reference to Firefly, and Harry doesn't get it. Meaning he made up that gag about Thomas off the top of his head.
Building up to the book's climax fight, Ramirez gets one while he's discussing plans with Harry.
Dresden: And if that wasn't enough, he's got an apprentice with him, called Kumori, who seems personally loyal. She's probably strong enough to be on the Council herself. Ramirez: Damn. She pretty? Dresden: She keeps her face covered. No idea. Ramirez: If she was pretty, I'd just turn on the Ramirez charm and have her eating out of my hand. But I can't take chances with that kind of power if I'm not sure she's pretty. Used recklessly, it could endanger innocent bystanders or land me in bed with an ugly girl.
"Life is a journey. Time is a river. The door is ajar."
Butters guilting Harry into making sure they got his polka suit out of the morgue.
"I'm not leaving it here for God-knows-what to mess with," Butters said. He grunted and threw a strap awkwardly over his shoulder. The bass drum rumbled. "Yes you are," I said. "We're not taking it with us. We don't have time for this." Butters turned to face me, his expression stricken. (Gilligan Cut) That stupid polka suit filled up most of the back of the SUV.
The conversation between Harry and Malcolm Dresden, when Malcolm warns Harry of the Jabberwock.