Oddly enough, Madison being saved from a monster by Frog!Daggeron was kinda awesome.
After getting de-brainwashed, Koragg/Leanbow's arrival when the Rangers are getting double-teamed by Megahorn and Black Lance. Centaur mode vs. chariot... dude.
Ditzy ex-villain Leelee, comic relief "troblin" Phineas, and apprentice sorceress Clare sneaking into the Underworld to get Udonna back. Phineas goes medieval on some Styxoids as the others can only watch openmouthed. Topped only by Leelee taking out the last one, which had gotten back up without Phineas noticing.
Phineas was the only character in the entire history of the show to literally wipe the floor with a defeated opponent. Good times.
Clare vs. Necrolai, though she did need her mother's borrowed power to do it.
In the same episode, two Styxoids get genre-savvy: one wishes he could go fight, the other talks about how the ones who do never come back.
Unmorphed Daggeron defeating Imperious... if you can buy it, considering how powerful Impy's been shown to be at other times.
The Gatekeeper sees the gate to the Underworld rise, demonic powerhouses break free, and Morticon (the early Big Bad) rampaging through the city. The Rangers confront him in their zords, and end up totally beaten. They collapse to the ground, powerless, helpless and totally overwhelmed. One of the Rangers murmurs softly, "Is this really how it ends?" to which Nick sets his jaw, looks up and says, "No."
In "Scaredy Cat," Imperious grows far larger than the Megazord and kicks the Rangers around, so Jenji matches him for height and takes him on.
Jenji: What's in my hands? Imperious: Foolish cat! Jenji: Wrong! (opens hands) Power Rangers! (Megazord slashes Imperious)
In Mystic Fate, once the Master returns, he immediately begins wiping out anybody who could oppose him. At one point, he shows up before the Rangers, drops the dead bodies of their team-mate Daggeron and Nick's father Lianbow at their feet, laughs, and leaves. At this point, Nick gives up. He has no idea what to do, is completely and totally out of ideas. To which Madison, the meek and soft-spoken Blue Ranger, turns to Nick and tells him, "No. You are our leader. You will not give up." Which leads to...
Nick versus the Master in the finale, after the Master has killed just about everyone who could've possibly stopped him.
Nick: Not here... NOT NOW ... THIS IS NOT OUR END!.
The Master: You are only one!
Nick: And unfortunately for you, the wrong one.
The final battle, when the citizens of Briarwood join hands to restore the Ranger's powers. Their belief in their heroes manifests itself as almost unlimited power, and as they chant, "We believe in magic!", they back away, the theme music kicks in, and the camera pans back to show all eight Rangers with their powers restored, invincible and unstoppable. In this troper's opinion, it is the only time ever that a role call in Power Rangers has actually been good.
For this troper, the scene gives me chills every time I watch it. It's so brilliant.
And years on, that morph is still seen as one of the best morphs in the entire franchise - including team up morphs.