Welkin drove his tank through the stinkin' RIVER to the enemy camp on the other side. The fact that he learned the appropriate spot where the water is the shallowest "by observing some weeds in the river" gives it a bonus multiplier.
The first launch of the Edelweiss. Many a fist was pumped into the air.
And Welkin again, in the ending. With the Marmota in flames and no way out for him and Alicia, and his troopers refuse to leave them and get to safety. His response?
In the Behind Her Blue FlameDLC; Johann running out into the battlefield under heavy fire to save Selvaria when she's been incapacitated by poison gas, in spite of his fears of being on the front lines. This action gets him promoted to an ace, and he becomes Oswald the Iron.
Edy in her DLC, first her decision to help defend the town, despite being outnumbered, and then later running from one side of the map to the other, through enemy lines, in order to save her "rival", Rosie, who's been injured.
In the same DLC, Homer actually pulls a subverted Cooldown Hug on her by slapping her in the face when she has one of her famous panic attacks when she learns that Rosie's in a bad way. How does Edy repay him? Slugging him in the chin, and then thanking him. Absolute genius.
Selvaria destroying Ghirlandaio using the Valkyria's Final Flame, blowing herself up along with an entire fortress and a good chunk of Gallia's main army in the process. It doubles as a Tear Jerker, and triples as a Dying Moment of Awesome.
Bringing down the Batomys super-heavy tank in Chapter 7, forcing the Imperials (including Selvaria in Valkyria mode) to retreat. Squad 7 does this by first destroying its MG turrets, then climbing on it and blowing up its radiators to disable it.
Let's not forget the snipers in that same chapter, who are capable of wiping out all of the starting foot soldiers on the first turn, as well the fact that they could wipe out Selvera's squad in a single turn as well(not including her of coarse.)