Max swinging down like Tarzan in the Die Hard on an X episode "Prodigy" and catching Logan as he's thrown off a roof.
"Female Trouble" is basically made of Awesome (and one of the few episodes not to have a Downer / Bittersweet Ending), but especially Max blowing Lydecker a kiss as she jumps over him on her motorcycle. Rule of Cool is in full effect.
Gem, the pregnant X5 in the Series Finale "Freak Nation," gets one of her own during the climactic siege at Jam Pony; one of the villains crashes next to her and she lays the baddie out with one punch... in the middle of her giving birth.
And speaking of the Series Finale, the entire final fight is a Crowning Moment Of Awesome for all the characters, but especially Joshua, who takes out two of the Breeding Cults most elite warriors, before nearly beating season Big Bad White himself to death, in an berserker rage. All the other transgenics struggled against a single opponent, whereas Joshua wrecked the joint and went back for seconds, without even slowing down, and then besting the main villain, a feat even Max on her best day had trouble pulling off.