Though it is only a small moment, Peter finally managing to produce Lux is pretty awesome.
Moon Over Soho
The magic battle on the rooftops between Peter and the Faceless Man: He threw a fireball at me. I threw a chimney stack at him that's the London way.
In that same fight, when the Faceless Man is trying to control the jazz vampires, Peter's narration off-handedly mentions that Tyburn would have had them on their knees by now. He even sounds smug about it, like he's proud in a way that the Faceless Man doesn't compare to Peter's Worthy Opponent. It shows how much Peter does respect her as a genuine magical force when they're not trading barbs.
Peter taking down the tigerman in the stairwell by giving him a facefull of Doc Martens and then surfing down the steps on his back was pretty awesome too.
An In-Universe example, this is Peter's reaction to Nightingale describing how he took on two Tiger Tanks in WWII by himself... and blew them apart.
According to another survivor in Foxglove Summer, Peter is not giving Nightingale enough credit. Taking out the Tigers were the least of his feats. Nightingale is described as being just shy of godlike in that battle.
Lesley managing to produce a werelight at the end of the book.
Although we don't get to see much of it, the battle between Nightingale and the Night Witch.
So as not to spoil an awesome scene, but said battle between Nightingale and the Night Witch include him unzipping the front of a barn as a distraction so he can walk in the back, doing something that made a cottage look as if it had been hit by a freight train and one or other of the two lifting the entire roof off the aforementioned barn and then bringing it back down. All of this without even creasing Nightingale's suit. Suddenly it makes much more sense why Nightingale was on rearguard at Ettersberg.
During the climax, Peter outsmarts the Faceless Man during their Rooftop Confrontation. The Big Bad jumps off the soon-to-be-blown-up building, using a spell to soften his impact. Peter jumps him and clings on, knowing that to shake him off, the guy would have to stop chanting, thus laying them both out for a rather rough landing, after which Peter goes to town on the guywith his trusty size elevens. He would've been able to take the Faceless Man in too, if that hadn't been the moment where Lesley finally gets to use her taser...
Peter uses a magic cane on a unicorn. The unicorns were terrifying for pretty much the entire book until that point. After that confrontation, the unicorn flinched whenever Peter looked at it funny.
The Hanging Tree
A nice one is the ironic rebuttal the Faceless Man has for Peter. Remember when Peter threw a chimney stack at him? Well, this time he starts a fight by throwing Peter's Asbo at him. That's one heck of a weight to use as a high-speed missile weapon.
One of the best has to be an off-screen moment. Nightingale finally confronts the Faceless Man, who attempts to kill Nightingale with a booby-trapped apartment, which is massive underkill for a guy whose combat experience is open warfare against the German military. Nightingale bypasses them and though we don't see it, it's implied that the majority of their fight is the Faceless Man retreating away from him.
William of Tyburn gets one when he hurls a sword from one building to another and nails a sniper right in the heart!