Individually, there were a few notable moments. Umbra and Nicholas being a Battle Couple and finally giving Lilith her comeuppance was satisfying.
Puriel beating down Oblivion and killing him.
We finally get to see why Etzel has an Expansion Pack Past. He's the most talented fighter of all the downworlders.
Seeing Dieter actually actively fight (and against the Big Bad no less) was pretty awesome. Yeah, he and Veronica didn't last long after Valentine went One-Winged Angel, but it was still pretty awesome.
The ending of the final battle. When Veronica does a Call-Back and brings back her bazooka, BigBertha, she uses it to blow Valentine out of the sky and trapped him in the Book of Red! Doubles as a Crowning Moment Of Funny.
Ethan shooting Valentine with Veronica's tank earlier in the battle counts too.
Leviathan's death. It's the first time most of the Resistance A) Actually meet for more than two seconds and B) They work together efficiently to take down a Greater Demon.
Can we not forget Nicholas's epic moment when he created a tornado of fire and wind that obliterated over half of Lilith's demon army in a single blast?
Umbra's Dying Moment of Awesome. Even though Death Is Cheap for his species, it was still pretty epic. This is a guy who has been a demon his whole life, and was imprisoned and tortured for over five thousand years just becauase he spoke his mind. Then he escapes, and everyone who meets him are terrified by him because of his Alwayschaotic Evil species, even the Resistance. He still accompanies them to Idris, and willingly gives his life in a heartbeat so that they can escape with the freed prisoners, knowing full well he'll go back to the Infernal Worlds to be tortured again. Could double as a Tear Jerker and Crowning Moment of Heartwarming.
Etzel's response to Dieter wanting to go back and save him was pretty cool too.
When Oblivion betrayed the Resistance, Puriel immediately attacked him. Ever since then, anytime the two fight it's a CMOA.
Bezaliel in the final battle. He's not much of a physical fighter, but he still wants to do something, so he lets out a battle song that calls all nearby downworlders, humans, and nephilim to the area to fight Valentine and take back Earth. He united all the species in one fell stroke after centuries of racism and hate. And then he goes on to try fighting Valentine anyways!