George O'Malley's very calmly delivered speech to a white supremacist paramedic is all the more awesome for the circumstances that surround it. It's given very quietly, very passively and slightly homicidally as he changes the dressing on the supremacist's wound. It's even more dramatic when you consider the first tenet of medicine is do no harm and the entire plot-line is whether or not you should let a patient's behavior dictate the care you give. George would.
George: Well, Dr. Bailey did save your life today. A black woman saved your life at great personal cost. So maybe next time you're looking at your tattoo, and you're thinking how much better all us white guys are than everyone else, you think about that. Because between you and me, if I had been alone in that O.R.? You'd probably be dead right now. (Leans in) And, uh, since we're sharing belief systems, I believe, if you were dead, the world would be a better place.
In the Season Two finale:
Adele: How dare you send those kids away? I just told my sister her baby's cancer's back, you're damned right I'm emotional. If you don't want to bend your precious rules for Camille, fine. Don't do it for her, do it for me. Do it for your wife who says nothing about your long hours, who looks the other way while you have an affair with another woman, who sobers you up when that woman left you, who stayed with you when everyone — EVERYONE — said I would be better off alone. I am not asking you, I am telling you. You're gonna make this up to Camille. You're going to prioritize the needs of your family over those of your other patients. Or. You're gonna find a new place to sleep.
Christina telling Meredith at the beginning of Season 5 what most of us have been thinking for years in one little speech… which is unfortunately undercut by the immediate Laser-Guided Karma that follows. Can be seen here.
In "The Time Warp" Bailey is shown to have been awesome even as an intern when she chews out her Jerkass attending for being too eager to operate instead of looking at the patient's history and symptoms properly.
The Season Six Finale brought with it quite a few of these, for quite a few characters. Special mentions go to Cristina, who manages to continue operating on Derek while a gun is to her head, among other things, and Dr. Webber for Talking the Monster to Death.
Teddy gets one too, when she blocks the cop trying to stop Owen from running back in to the hospital to be with Cristina.
As does Jackson, who unplugs Derek from the monitor when the shooter is taking out Owen, thus fooling him into thinking Derek has died.
George saves a patient in the elevator after earning the nickname 007.
In season 7 episode 11 "Disarm", Christina comes out of her Heroic BSOD by following a group of ambulances to what turns out to be a mass shooting at a college; she then saves a man's life by cutting open his chest and using her own hand to stem the blood in the ambulance', and she stays with him and participates in the surgery when they get him into the Seattle Grace OR. Made even more awesome by the fact that the patient in question was the shooter.
Karev saves a 15 year old girl's leg by physically blocking Dr. Stark who was about to cut it off needlessly.
The episode ends with a moment of awesome for the whole cast. Dr Webber announces that they received 26 of the victims and none of them died.
The "letter of recommendation" Bailey delivers about Meredith in the season eight premiere.
Season eight, episode four, Owen ordering an OR for a broken jaw, then producing said broken jaw by knocking a man twice his weight unconscious in one punch. Then later on explaining to him that no, he won't apologise, and that hurting his patients and his staff is not acceptable. All after being made Chief of Surgery a few episodes prior. Papa Wolf or what?
Towards the end of Season Eight, the five residents have to take their Board Exams, and April, err, let the stress get to her. Resulting her attacking a cocky rival via body blow. And starting a barroom brawl. Who'd've thought that tiny thing had it in her?
April threatening to run Dr Hunt down with an ambulance when he was giving them lessons in trauma surgery.
Every single interaction between Cristina and Dr.Thomas.
George's Heroic Sacrifice: He pushed a girl out of the way of an oncoming bus and got hit instead.
When Bailey is given an ultimatum by her first husband, he threatened to divorce her if she took the pediatrics fellowship which would require longer hours, telling her to become a general surgeon instead. She took a third option, leaving him because she didn't want to be with someone who would give her ultimatums, though she decided to do general surgery since the divorce meant she would need to spend more time at home to take care of their son.
A nerdy teen gets himself encased in a block of cement (to impress some popular kids and his crush) and, while everyone frantically tries to get him out, he calls himself a loser and compares himself to Han Solo frozen in carbonite. Dr. Bailey assures him that neither he nor Han Solo is a loser, and then lists all of the awesome things Han Solo has done-including in the Expanded Universe. When she's done, everyone is staring at her and she just says, "I like science-fiction. Anyone got a problem with that?"