In episode 8, Akari finally resolving to pursue the title of Jewel Star Grand Prix champion, after spending the previous episodes saying she couldn't do it.
Every spell Alma and Leon cast could count as this, if only because they look so freaking cool doing it and the animators really splurge their budget when they have to animate spells.
In episode 28, Miria's song which recovers Garnet and Sango from their fever. And, she gets a star for it!
And in episode 42, Miria's selfless words of encouragement to her friends, which win her the last star she needed for the Grand Prix.
In episode 33, after going through a lot of drama involving her sister and Yuuma, which almost rendered Akari incapable of using magic again, she manages to confess her feelings to Yuuma (if somewhat laterally) and strengthens even further her resolve to follow her dreams, which manifests in this awesome show of magical power as she flies through Jewel Land.
The duel episode between Alma and Leon in Episode 47. It is probably one of Studio Comet's best animated fight scenes ever done.
Kanon, Jill and Shouko walking out alive, almost got burned after the building that they were imprisoned in got destroyed. With a little music.
It can't be denied that episodes 49-52 had some pretty kickass fight scenes. Like mecha-Garnet vs. mecha-Sango, Labra vs. Master, Peridot vs. a horde of Mooks, and especially every Jewelpet in existence vs. Dark Jewelina.
The final battle in Episodes 51-52. Not only the Kira Deco 5 gained their Eleventh Hour Superpower moment, but Ruby restored the Mirror ball in its original state and defeated the Dark General.
Mouri's Archery scene in Episode 12. Seriously he stood up to Apel's challenge and shoot the Sakuramochi in a serious point-blank position.