In the first episode, Walter, upon seeing three men, stronger than him, teasing his son in a store, left the store, walked around it, reentered it, and kicked one of them in the back of the leg. He then proceeded to face the three down, and get them to back off.
Blows up an asshole lawyer's car with a squeegee across the battery. Even the other people who see it don't even bother to help him put it out as Walt just casually drives away.
Blows up Tuco's den with a few crystals of fulminated mercury, aka mercury (II) fulminate, aka the stuff that makes some types of gunpowder in a cartridge go "boom!" As a notable piece, this came in the scene after Walt shaved his head bald.
And who could forget episode 3, where Walter has to decide whether or not to kill Crazee 8 and realizes that Crazee 8 is planning to kill him with a broken shard of plate. Rather than use gunfire, a knife or simply letting him starve, he chokes him to death by pulling on the bike lock holding him by the neck to the pole.
The way he came to that decision was pretty awesome as well. By being able to deduce that Crazy8 was going to kill him, by scavenging the pieces of the broken plate from the garbage and seeing a large piece was missing.
The moment that convinced this Troper to watch the whole series was in episode one when Walter, at gunpoint and in all likelihood about to be killed by the drug dealers once he finished the batch of meth, secretly whips up some phosphorus hydride.
It's a pretty grim moment of awesome, but the season two finale, when the tragic ending that's been foreshadowed all season turns out to be a brilliant piece of misdirection by the writers. Also Skyler's exit speech. Wow.
Walt's badass stroll out into the parking lot in Over as TV on the Radio's "DLZ" plays in the background, culminating in the coldly delivered line, "Stay out of my territory".
Jesse vs Tuco and later Hank vs Tuco.
The Cousins walking away from an exploding truck without flinching. One of them even starts smoking a cigarette.
In the season 3 finale Mike storming that warehouse and killing those guys with the silenced pistol.
Hank's little "bet" with Marie late in Season 3. The faces as they walk out cements it as one of the funniest things in the known universe.
The pizza toss. Made more awesome by the fact that Bryan Cranston nailed it on the first take.
Gus pushing exactly the right buttons to get Walt back to cooking, talking about how a man provides for his family no matter how little they appreciate it.
Hank vs. The Cousins. Hank kills two characters shown to be axe-wielding mass-murderers with only one minute's warning. And he's unarmed to begin. And he manages to survive multiple gunshots to his torso. And he kills the 2nd cousin after being shot to hell. Holy Shit.
His "The Reason You Suck" Speech after Walt tries to hire him back as a partner, about how his life has been systematically destroyed ever since Walt came into it. A fantastic acting moment and something Walt really had coming.
Gus' plan to take out his Mexican opposite number and take over the whole operation. Especially impressive in how fast he was able to put such a complex plan together, and have it work perfectly.
Skyler coming up with a complex cover story on the spot about how she and Walt are in a position to pay Hank's medical bills, even integrating Walt's "fugue state" ploy.
In the final scene of "Half Measure", Walt runs over two gang members before they could kill Jesse. He then takes the gun from the survivor and shoots him in the head. He tells Jesse to "Run!" OH MY GOD!
In "Full Measure", just when it looks like Walt is selling out Jesse, it turns out to be a very nicely played gambit, and that's putting it mildly. YEAH...
"Fly". Bottle Episode or not, don't you dare say that the titular fly falling dead at Jesse's feet isn't awesome.
In the premiere, Skyler figuring out exactly what Walt's been up to the last two seasons. Walt's stunned.
Gus' first non-flashback appearance in the premiere. Every. Single. Second. Of it.
Jesse also has to be recognized here: As Walt is struggling not to vomit, Jesse, who's been catatonic for the whole episode after killing Gale, looks at Gus with an unflinching "bring it on" gaze. Badass.
Mike calmly listening to Walt's case that they should team up to kill Gus, and then walloping him right in the middle of the bar without a word.
Skyler swindling away the car wash Walt used to work at to use to launder their drug money, for less money than she originally offered and telling the owner straight out it's because she doesn't like him.
Mike killing two Cartel gunmen who attack a shipment, followed by simply acting slightly annoyed when he realizes part of his ear was shot off.
The Cartel gets theirs back when they try again; this time the hitmen pump the truck's exhaust into the trailer and wait for the guards to die, munching on the driver's lunch.
Walt demands his old boss leave behind the first dollar the car wash earned ("As is"). He cracks open the frame, takes the dollar and uses it to buy a Coke.
Hank figuring out Gus' role in things by following a seemingly ridiculous hunch and tricking Gus into pretty much giving him his fingerprints.
"I AM THE ONE WHO KNOCKS!"
Gus' Unflinching Walk through a hail of bullets, and daring the Cartel sniper to kill him.
Preceded by Mike pushing Jesse away from a bullet at the last instant.
Gus killing Don Eladio and all his capos with poisoned Tequila. To get them to drink it, he first has to drink a shot himself, then lets slip nothing for a while afterwards, until he finally asks to use the bathroom shortly before the poison will take effect so he can throw it up. And even when he's alone, he still goes through the process as calmly and methodically as possible. Afterwards he starts feeling some of the effects, but still manages to shout to the survivors that their boss is dead, so they should just grab some stuff from the corpses and leave. He's pretty much becoming a bigger Magnificent Bastard with every new scene by now.
The scene also includes Mike garroting the Cartel's sniper, and Jesse gunning down the one Cartel member left before driving away with the seriously wounded Mike and poisoned Gus.
After Gus recovers, he makes sure to visit Don Salamanca's nursing home to make sure he knows what happened, and who it was who did it. He tells him that Jesse killed the only blood he had left on earth, and the cartel he worked his whole life for is exterminated. An incredible example of Best Served Cold I've seen, especially since Don Salamanca is the one who killed Gus' best friend and surrogate brother.
Jesse talking down to a Cartel cook who could very well kill him at any moment, lambasting him for having a filthy lab and inadequate preparation for Walt's and his meth. While Gus and Mike allow themselves the slightest of grins.
Walt's Kansas City Shuffle over the season's final two episodes, getting Jesse back on his side by first incriminating himself and then "proving" himself innocent, then working with Tio to take care of all possible loose ends. Followed up by brutally gunning down the man holding Jesse hostage, and the two of them burning down the Superlab, the source of all their problems. It's not often that crossing the Moral Event Horizon intersects with a CMOA, but there it is.
Even more awesome with elaboration: Walt finally kills Gus by convincing Hector'Tio' Salamanca to act as a suicide bomber. When Walt declare "I won", he frigging means it.
When Tio is about to trigger the bomb it first looks like he's trying to smile and then he gives a look of pure rage to Gus seconds before the bomb detonates and Gus gets half of his face blown off.
Gus himself standing up, walking out of a room, and straightening his tie. With half his head missing.
Walt talking to another man about being diagnosed with cancer:
Walt: To hell with your cancer. I've been living with cancer for the better part of a year. Right from the start, it's a death sentence. That's what they keep telling me. Well, guess what? Every life comes with a death sentence, so every few months I come in here for my regular scan, knowing full well that one of these times - hell, maybe even today - I'm gonna hear some bad news. But until then, who's in charge? Me. That's how I live my life.
YMMV. Walt is trying to convince the guy as much as he tries to convince himself. At the point in his life he says that, NOTHING is in his control.
Jesse driving in a go-kart track, taking out his frustration, while yelling at the top of his lungs. It sends shivers down one's spine.
Even the promo for Season 5 contains one. Saul is trying to quit as Walt's lawyer, when Walt stands, gets in Saul's face and growls "We're done when I say we're done."
The season's opening scene: a flashforward where Walt makes an illicit deal which leaves him with a car key. Then it turns out he was actually buying what was in the trunk of the car: a freaking M60 MACHINE GUN.
Jesse actually gets to save his, Walt's and Mike's bacon with his Crazy Enough to Work idea of using a junkyard magnet to erase Gus' laptop while it's in the evidence room.
He tops this with his idea to rob a train, without anyone ever knowing.
Mike getting the drop on another hitman by leaving one of his granddaughter's toys knocking against the door.
The crew needs to come up with a way to cook while hiding in plain sight. So Walt comes up with the most brilliant, most audacious idea ever - they create a mobile lab and cook in other people's houses, posing as a pest control company.
Skyler telling Marie what the entire audience has wanted to tell her since the series began: "Shut up! Shut up! Just shut up!"
YMMV. If it was the other way on the other hand...
When Walt goes completely Heisenberg on Skyler, tearing down each of her plans to protect their kids from him, she finally shuts him up by simply stating that her only real plan is to hold out and hope his cancer comes back. And 90% of the viewers voted that they agreed with her.
Also, her awesome jab: "I thought YOU were the danger."
"Dead Freight". Two words: train heist!. Totally successful one too, up until the last minute of the episode where Todd shoots a child witness
Walt MacGyvering his way out of zipcuffs with an exposed wire from a coffee machine, which he holds on the cuffs until they break even as it also burns his wrist.
Todd getting punched by Jesse counts after Todd tries to rationalize shooting a child dead.
"Say My Name":
Walt's deal to keep his meth business while making his competitors into his employees, culminating in a killer Say My Name moment. "You're goddamn right."
Mike's "The Reason You Suck" Speech to Walt, and after this drives Walt to shoot him, his last words are still telling Walt "Shut the fuck up, and let me die in peace."
Walt and Jesse arguing about Jesse leaving the meth trade, culminating in Jesse walking out while Walt yells at him.
"Gliding Over All" gives us two memorable montages:
All ten "loose ends" getting killed in prison in increasingly brutal fashion, including one being burnt alive. All of them are pulled off in the space of two minutes.
Walt and Todd pulling off multiple cooks while Lydia cooperates with sending their meth business off to the Czech Republic.
"You got me!" and Hank's look of sheer disbelief afterwards.