All hail Frank Bryce, the only Muggle to mock Voldemort towards his face. True, he did die, but the old man had balls of steel, befitting of a World War II veteran.
"Lord, is it? Well, I don't think much of your manners, my Lord. Face me like a man, why don't you?!"
Cedric, Fleur, Krum, and Harry in the first task of the Triwizard Tournament.
In the second task, Harry stubbornly refuses to leave other prisoners; he comes in last but is awarded second place for his "moral fiber", as Fred and George put it, and more importantly wins respect from the other competitors.
Harry and Cedric deciding that it didn't really matter which one of them won the tournament, instead just doing it for the honor of Hogwarts. In hindsight, this may not have been such a good idea.
Yes, that's right - Snape gives a "F*** you!" to the Minister For Magic and gets off scot free!
The first task, where Harry uses his Quidditch skills to face against the dragon and get her egg. Even the judges weren't expecting it.
Bagman's reaction; particularly this bit once you realize who's being told to see Harry in action:
"VIKTOR KRUM ARE YOU WATCHING THIS?!"
Barty Crouch Sr. walking from his home all the way to Hogwarts, while fighting indoctrination by the Imperius Curse the entire time. When Harry finds him, he's barely hanging on to his sanity, but the fact that he was able to do that speaks to some immense willpower. The best Harry, one of the very few people shown to be able to resist the Curse, was able to do was a few seconds, and Junior could only manage a few moments at a time.
When Harry stepped forward to face Voldemort. He knew that he was about to die. But he would not die crawling and begging for mercy. Daniel Radcliffe's expression for that moment just sold it. Completely.
Harry vs. the Horntail. The book has the Horntail just guard the golden egg, and stay in the arena. In the film, the dragon breaks free from it's bonds, and chases Harry throughout Hogwarts, including across more than a few roofs. Harry gets the upper hand by doing what he does best on a broomstick; swerving at the last second where no else could have, making it too late for the dragon to veer away and smashing into the bridge, momentum flinging it down below. Plus the special effects are absolutely amazing.
The Dark Mark. In the book, it's described as basically a green constellation shaped like a skull vomiting a snake, but in the movie, it's much cooler and dynamic-looking. Not to mention, Death Eaters apparate out of it.
Snape making Karkaroff figuratively and literally shit himself with one simple line:
Snape: I have nothing to be scared of, Igor. Can you say the same?