Almost every girl gets her Enchantix in a Crowning Moment of Awesome.
Flora: One of the Trix (I think Stormy) fires an attack at Flora, but her little sister Rose/Miele jumps in front of her to protect her. Rose gets knocked into the poisoned river. Flora gets angered so much that she creates venus gobblers to swallow the Trix, then dives in the river after her sister and saves her. She not only achieves her Enchantix, but after she appears out of the water, she uses her fairy dust to make the weeping willow grab the Trix and throw them into the river. (Rose protecting Flora can also qualify as a CMOA since she's so young)
Stella: Protects her father from a raging dragon, using so much power that she almost loses her life.
Musa: Darcy sets the Alfea library on fire. Princess Galatea of Planet Melody refuses to leave without the important books/scrolls that the Trix were trying to steal. Musa goes to save. Galatea tells her to just leave her and save herself, but Musa refuses. It's actually her will to save Galatea that earns Musa her Enchantix.
Bloom: Since Bloom was the last of her kind, she believed that gaining her Enchantix would be impossible, but while she's training on Pyros, the island of dragons, she is attacked by the Trix. During the fight, she manages to focus all her energy on one point, and manages to gain her Enchantix (although two episodes later, it is revealed that her Enchantix is incomplete since she didn't gain it from sacrifice) and proceeds to defeat the Trix, chasing them off.
Bloom in Episode 3. Icy is berating Bloom for apparently not having any powers and just when she's about to kill her, Bloom manages to transform into her Winx by believing in herself.
S4 episode 18, the Specialists try to challenge Diana, the powerful nature fairy who has turned Gardenia into a jungle. However, Nabu is the only one who can actually put up a fight against her, and pretty much ends up having to fight her all by himself after she defeats the other Specialists. While he wasn't able to stop her from kidnapping the Specialists at the end, he didn't get hit by any of her attacks during the fight, and he took down at least two plant monsters she had created.
Season 1, Episode 7. The girls' powers have been temporarily revoked as punishment for sneaking into Cloud Tower. While everyone else in the school (staff and students) is away at a concert, the girls call the boys over to help them clean up (part of their punishment) and afterwards, they throw a party. The Trix, in an attempt to capture the dragon fire, summon a minotaur to crash their party. Despite not having their powers, the girls actually manage to defeat the monster (with a bit of help from the specialists, but the girls do most of the work). Obviously, powers or no powers, the Winx are far from weak!
Roxy gets one in Episode 4x12. After Gantlos injures Artu (her dog), he tells her that he's only a dog and she shouldn't be upset. Roxy is so enraged by this that she unlocks her full fairy form. Then she summons a hoard of mice to Zerg Rush Gantlos. He does break out and blast her out of the shed but still, it's not bad for a first-time fairy.
In episode 2x25, as the Winx and Specialists are trying to get to Lord Darkar's lair so they can rescue Bloom, Sky's airship is damaged and he's unable to fly straight. Seeing as Sky is unable to get his ship back into the hangar of the large airship being piloted Riven and Helia, Helia decides to use his laser-string glove to reel Sky's airship into the hangar of the ship while it's still moving. And he succeeds.
The very first episode, when Bloom's power awakens after Knut grabs her. She may not have done it on purpose, but still, it was pretty awesome.
Virtually every time Faragonda battles. Especially when she's on her own. That woman can kick some serious butt.
Tecna having survived in the Omega Dimension. We're talking about what's basically a frozen wasteland that is supposed to be inescapable. In fact, if I remember correctly, she even said she was able to turn ice into food so she could survive.
The three times Bloom (accidentally) releases the dragon fire in rage. The first time was when Darcy was about to kill Musa, the second time was when Icy had seemingly killed Kiko and the third time was when one of the witches (Icy again, I think) had turned Mirta into a pumpkin. Depending on how you look at it, it could also be seen as heartwarming in that all three times, the trigger was the life of someone she cared about being endangered.
In S5 E7, Tecna manages to outsmart Darcy's darkness bubble by summoning X-ray vision goggles. As if that isn't cool enough, she hits Darcy perfectly after using the X-ray vision!
In the same episode, Bloom, Stella and Aisha must face an illusion conjured up by magical shells based on their inner fears in order to learn the location of the Gem of Self-Confidence. Aisha's is an illusion of Nabu, that accuses her of letting him die when she could've saved him. Aisha almost immediately sees through the illusion, since she knows the real Nabu never would've said that to her, and then helps Bloom and Stella deal with their illusions.
From the first movie, Mirta's reaction when Mandragora and an army of monsters attacked Alfea and one of those had apparently killed a teacher was of blasting the monster away and cast a spell of the freakin' Ancient Witches Coven to kill it. Ok, she didn't get to complete the spell as the teacher was revealed to be alive and destroyed the monster by becoming an elephant and sit on it, but it was still awesome, especially as the other fairies were running away and keeping in mind that in season one a monster like that could give a Specialist a run for his money.
In the second movie we see Oritel in combat against Darcy and Stormy. With his sword temporarily depowered due the Trix and the Ancient Witches sealing away all positive magic you'd expect him to be at their mercy... And instead, they are barely a match to him (and he nearly killed Stormy with her own thunder in the first moments of fight). Made even more awesome because he then leaves to chase Icy, and Darcy and Stormy proceed to effortlessly kick the asses of the Specialists (plus a Brought Down to Normal Nabu, but without Sky) and the depowered Winx (minus Bloom).
Later his sword's power is restored. The Three Ancient Witches' reaction when they see him attacking? Oh Crap, and he proceeds to fight them to a standstill, when the Winx with their powers restored were getting their asses kicked hard.