The Super Zeozords' debut battle, particularly Super Zeozord 5's fight. It chases Silo II into low orbit, casually blocks his missile barrage, and then runs him through. Then they all form up for a victory flyby.
The Super Zeozords follow up on that with the debut of their Megazord configuration. The Super Zeo Megazord wrecks King Mondo's sword, raises its own swords over its head, and touches them together, forming an absolutely enormous Laser BladeBFS that it brings crashing down on Mondo.
In "King for a Day, Part 2," Bulk and Skull (who were teleported to another planet) meeting a One-Shot Character who had been imprisoned by Gasket for some time, passing themselves off to him as great warriors, then successfully fight off a number of Cogs. And just to add to how awesome this is, the Rangers preferred to be morphed while fighting Cogs.
The Impursonator is one for Rita. It. Beat. The. Zeo. Ultrazord. Holy shit.
This was also the only encounter in which Zeo Ultrazord used it's "second configuration" for a round two after the common configuration's Beam Spam was blasted back at it. Pyramidas basically acted like a sled for a lineup of the original Zeo Zords, and fire off even more Beam Spam (which didn't work.) This was something people thought only the toy would ever do, but the moment of awesome was kind of lost because HOLY CRAP did the Ultrazord just run away?!
How about that last episode, eh? The Rangers grow to Ultraman proportions to battle King Mondo, and after that? The original villains blow the Machines up with a false peace offering. What a way to end a series.
Zedd: We're back!
Jason's surprising return, as the new Gold Ranger.
Trey's introduction scene as the first Gold Ranger screams sheer epicness. He blasts down Wolfbane and charges the Cogs wiping them all out (accompanied by his awesome theme song) saving Tommy and the other Zeos. Also, when Wolfbane grows huge, Trey just summons his humongous Pyramid zord and zaps him into oblivion. That's how you properly introduce a sixth ranger!
GOOOOLD RAAAANGER!! GOOOOLD RAAAANGER!! GO GOLD RANGER!