From the pilot: In his first fight with the Red Lanterns, Hal exhausts his ring's power supply. He then leaps off of a cliff, lands atop his ship, recharges his ring on the ship's engine, and blows away the Red Lanterns with a giant beam of Emerald Energy. Oh, and the music for that scene is pretty cool, too.
Bonus points for saying the Green Lantern Oath in about five seconds, timing the finish right as he strikes the ship engine and he didn't even stumble on his words!
Hal's Cruel Mercy to Razer. Instead of taking the bait Razer desperately wants him to take, Hal takes Razer prisoner, and tells him point blank that Razer will have to make amends for what he's done. When Razer calls him a coward, Hal punches Razer out, then takes his Red Lantern ring. Don't fuck with Hal Jordan.
In "Reckoning" Razer blasting Atrocitus and rendering him unconscious after the latter revealed he'd caused the wars on Razer's homeworld and killed his wife to make Razer a Red Lantern.
Also in Reckoning, the VERY biased version of the history of the formation of the Red Lanterns.
Atrocitus also has a very good one when he proves clever enough to not let Razer actually recharge his ring, knowing he would try and assassinate him. He plays along and Razer's assassination attempt ends in complete failure.
"Regime Change", all of it. The kicker is the finale, though. Ganthet activates his secret weapon he hid on the Interceptor, a Blue Lantern battery. This releases a wave of hope which supercharges the Green Lanterns taking part in the battle. They then proceed to utterly mop the floor with the attacking Red Lanterns. This is followed by them using their supercharged rings to launch a self destructing tower into space!
At the end, the Blue Lantern battery travels into space. It's revealed next season that indeed, the Blue Lantern Corps were soon to begin.
In "Invasion", Aya manages to fly through a forcefield beam being generated by the Lighthouse in order to get around the Red Lanterns guarding it, then turns the same defense systems which kept the Interceptor at bay on the Reds. Hal has nothing but praise. Too bad Atrocitus managed to reprogram her later.
Saint Walker climbing a mountain in search of a savior, and when he reaches the top he seemingly found nothing. And instead of giving into his despair, he refused to give up hope and would keep searching for a way to combat the Red Lanterns. The Blue Lantern of Hope flies down to him, and he sees himself in its reflection as the first Blue Lantern Ring appears out of it.
For additional awesome, Saint Walker proving his hope inextinguishable. He spends the majority of the episode seeking a "savior" that Mogo once told him of and finally surmounted the mountain only to be met with no savior at its peak. In spite of this and his assumption that Mogo was trying to teach him that there is no savior and no hope he refuses to fall into despair and in doing so calls the Blue Lantern to him, and as the ring presents itself he sees himself reflected in the lantern. The Savior was him. It was always him.
Atrocitus earns one this episode as well, when he :completely outgambits Hal Jordan. After escaping the Maelstrom, he tricks Hal Jordan, Kilowog and Razer unto his seemingly damaged battleship, which he has abandoned and which self-destructs. While that happens, he hijacks Aya right under their noses, which allows him to travel instantly to a vulnerable Oa. Then he finally blows a tunnel in the Maelstrom with the Liberators he left behind, thereby making way for his armada. Pretty impressive to say the least.
Kilowog in "Home Coming". He stands alone to hold back the Red Lantern Armada. He knows perfectly well that he's going to die and what does he do? Bring out his battery and recharge his ring for the last time. Never has "No Evil Shall Escape My Sight" sounded so awesome.
Carol immediately taking action to save Hal from an amnesia induced from being transported to Earth by the Star Sapphires.
Saint Walker's Establishing Character Moment as a Blue Lantern is to punch out a Red Lantern warship. That is entirely literal. He punches it, sends a pulse of Blue light into it and it's immediately disabled.
Saint Walker and Mogo pulling a Big Damn Heroes moment to save Kilowog and wipe out the Red Lantern fleet. Especially when Saint Walker channels the full force of Mogo's Wave Motion Gun through his ring for the finishing blow.
Hal, after receiving a vicious pummeling from Atrocitus, gets his Heroic Second Wind and proceeds to utterly kick to his ass.
Appa Ali Apsa accepting the fact that the Guardians were responsible for the tragedy that befell the Forgotten Zone and promising to make restitution.
Guy Gardner and Hal having a Green Lantern smackdown during "The New Guy".
When they finally get on the same page during the fight with the Manhunters, and proceed to mop the floor with them via Combination Attacks.
Tomar-Re becomes the first Green Lantern to bring down a Manhunter solo, by stabbing it in the chest with a trident then firing beams from the tips to blast it apart.
Aya uses the full might of the Interceptor on the Anti-Monitor. It knocks him down. That's all it does.
"Steam Lantern": Hal pulls a planet through a crack between universes in order to save its people, with a barely-charged ring at that.
"Blue Hope" is a string of such moments.
Saint Walker and Brother Warth teaming up against a Manhunter, Hal and Kilowog tag-teaming a Manhunter near the end, Razer getting Saint Walker to Summon Bigger Fish, and finally Razer utterly destroying a Manhunter who shot Aya.
The last was particularly impressive. The power of the Blue Lanterns tend to cancel out the abilities of Red Lanterns. Razer even points this out earlier in the episode. When a Manhunter fired on Aya, his rage overwhelmed the negating abilities of the Blue Lanterns and allowed him to completely destroy his target. This also convinces him that he CAN use his anger for good, so long as that anger is righteous.
Razer's kill is also notable in that his rage manifests less as brute force, as most red lantern maneuvers do, instead utilizing precision Razor Wire.
Ganthet starting up the Central Blue Lantern Power Battery is an amazing sight: he floats towards it, eyes glowing blue, recites his fledging corps' Badass Creed and the battery roars to life. A blue energy wave radiates from the planet as if heralding a brand new era.
From "Prisoner of Sinestro", Sinestro demonstrates exactly what kind of person he is. He shuts off the oxygen around the ship, forcing the mind jumper alien to go back to its body, as its cell is the only place that has air now. And then he reveals that it was damaged in his breakout, lets the alien die to spare them the trouble, and then lies to Hal, saying that his body must have suffocated before he got back. He might remain a good guy throughout the entire episode, but he's still Sinestro.
Razer tearing through Manhunters in "Loss" while extremely outnumbered. And when three do finally do get the better of him, Aya destroys them in a single shot.
Throughout the episode, the crew of the Interceptor basically flip the Science Director off at every opportunity: Razer and Hal confront her about trying to destroy Aya, Aya non-verbally tells her to shove it when she tries to order Aya to abandon Razer, and Hal outright disobeys her to save them both not long after.
Even if it massively went downhill right after, there's no denying that Aya killing the Anti-Monitor was awesome.
Hal grabbing a severed Manhunter head off a giant beast's chest and charging his ring off it, while being swallowed by the beast.
Hal's motivational speech to Kilowog and Razer:
Hal: We're not Lanterns because of these [gestures with his ring hand], we're Lanterns because of this [points to his heart] and this [points to his brain].
Amusingly, they didn't understand a word of what he was saying.
After Carol gets wrangled into a Forced Prize Fight with Atrocitus and summons Hal for some muscle (she tries, but he's been at it longer), Carol gets one very good hit in. With a giant boulder.
Hal's beatdown of Atrocitus just prior. Never a good idea to threaten Carol.
"Larfleeze": Appa gets one at the beginning, chewing out Hal for creating the Aya mess by allowing her to evolve and rescuing her from decommissioning.
Hal for taking all the blame without comment, and agreeing that they need to stop her.
Larfleeze himself proves to be quite the Determinator, attacking Hal, grabbing his battery and not letting go while he flies around and clobbers the others. He even jumps on top of him later, and starts pummeling his face.
Hal fighting off the influence of the Orange Lantern.
The entire Green Lantern Corps vs Manhunter fight, which ends when Aya descends personally and knocks them out. Then she has the best Kick the Son of a Bitch moment in the series when she murders the Not Quite Dead Anti-Monitor.
The Green Lanterns vs the Manhunters, round two. Moments include: Ch'p yanking the head off a Manhunter, the return of Kilowog's machine guns, Larvox using his swords, really the list goes on and on.
The end, where Razer flies off Oa alone to find Aya, or what is left of her. He disappears into the stars, and just when the viewer thinks it is the final shot of the series a Blue Lantern ring drifts onscreen and follows him.