In A Darkling Plain they successfully recreate magnetic levitation technology while living in the ruins of London. It turns out to be a major factor the much brighter future we see in the Distant Finale
In Fever Crumb: When half of London is rioting outside their compound demanding Fever's head the first thing they do is calmly and effortlessly hold off an entire city with an electric fence. Then when Fever offers to sacrifice herself for the good of the guild they immediately refuse. By the end of it they launch Fever to safety on a hot air balloon they were working on, possibly the first working flying machine since the apocalypse, while their home is burning underneath them. Then they calmly walk down the fire escape, disguise themselves and walk away.
Nimrod Pennyroyal gets one near the end of the fourth book. He killed the Stalker Fang. Yes, him. He can't believe it himself.
Most of what General Naga does is pretty awesome, but the absolute standout is flying a burning airship into the mouth of Harrowbarrow in a magnificent Taking You with Me.
