Heartwarming / Harry Potter and the Chamber of Secrets
From the Book:
When Dumbledore finally learns that Harry has been Wangsting that he was only fit to be in the house of Slytherin, the so-called "house of villains." That moment, when Dumbledore proves to Harry that he is better than he gives himself credit for, is a truly magical one.
Ron, Fred and George showing up to rescue Harry from Privet Drive and bring him, home. If that's not real friendship then I don't know what is.
When Ron, Fred and George bring Harry to the Burrow for the first time, while Molly is furious with her boys for sneaking out and taking the car to get him, she immediately welcomes Harry into her home and offers him breakfast.
Not to mention, she mentions that she and Arthur were seriously considering going to get Harry themselves. If anything Ron and the twins just ripped the bandage off.
The most surprising thing about the Burrow, to Harry, is that everyone there likes him. Molly dotes on him, Arthur wants to learn all about Muggle life, Ron is his best friend, Ginny's got a crush on him, and the twins just love to goof off with him. To someone who's only really known a home life of cruelty and abuse, this must have been the most amazing thing in the world.
This was a small one, but when Harry and Ron are about to sneak away from class they run into McGonagall. Harry tells her they were going to see Hermione, who is still petrified, and McGonagall lets them go. McGonagall, one of the sternest, strictest, no-nonsense teachers at Hogwarts, tears up and lets them go see their friend. And in the end it is this visit that helps them solve the enigma.
Harry telling the man who murdered his parents and is about to murder him and his best friend's sister that Dumbledore is a better wizard than Voldemort. That is demonstrating courage worthy of Gryffindor House.
While it's mostly funny, Fred and George doing their "Heir of Slytherin" routine when people think Harry's the Heir of Slytherin. Especially since it actually cheers Harry up a little bit, since he knows Fred and George are being sarcastic and are among the group who DON'T think he's the heir.
A very brief moment, but Percy gives some simple, sincere advice to Harry when the latter is choosing his course list for third year; no condescension and almost no bluster. Granted, Harry doesn't consider it helpful, but points for trying.
At the end of the novel, Ginny of course blames herself, despite the fact that this is in no way her fault. And Dumbledore tells her as much, getting her some hot chocolate and assuring her that she's not the first (or, sadly, the last) to be conned by Lord Voldemort, and that no punishment will come to her.
Chocolate is the cure for a Dementor attack, ie having something feed on your soul... which is exactly what Riddle did to Ginny. That mug of hot chocolate probably did more that just reassure her.
When Harry gets called to talk to Dumbledore after the attack on Justin and Nick, he worries he's going to be accused. Apparently Hagrid had the same worry, because he immediately bursts in swearing up and down that he was with Harry only minutes before the attack, and he'd swear in front of the Ministry itself if he had to. Granted, that's not at all what Dumbledore wanted, but it's still sweet.
After it's revealed that Harry is a parseltongue, Ron and Hermione drag him away to have a serious chat. While they're worried about what other people will think about it, they are not worried for a moment that Harry might actually be the Heir Of Slytherin and dangerous. The idea that they might not stand by their friend? Doesn't come up at all.
Dobby and Harry's relationship. Dobby can't turn against his master, and will have to punish himself for everything he'll do to help Harry, even if they don't know about it, and will do it himself. He still does it, going as far as going the closest he can to reveal who the culprit is the very first time he meets Harry. Without Dobby, Harry would have started reacting too late, Voldemort would likely have been resurrected that year, and the basilisk would still have been alive and at his orders, what stopped him was the humblest of creatures ready to face all the pain he'd have to endure to help a little child. And then, there's how Harry repays him. Not only Harry's very survival helped Dobby (house elves' lives are horrible, but Dobby reveals they were much, much worse under Voldemort), but he also treats Dobby like a person. Keep him mind, not only he doesn't know him, he doesn't even know what house elves are, and still he treats him as his equal from the very first time they met. That's what earns Dobby's Undying Loyalty that will last through the whole series. Not too mention that, despite everything Dobby put him through and made him endure, Harry still took the first chance he saw to grant him freedom.
From the Film
"There's no Hogwarts without you, Hagrid."
At the final feast of The Chamber of Secrets, Hermione races the length of the hall to hug Harry and has an awkward reunion with Ron. Then, Dumbledore makes his speech — but, what's this? A door opening! Who dares to interrupt the great and Powerful Dumble— Oh, It's Hagrid! Carry on! Cue the biggest load of tears (up to this point!) that anyone will ever give as, the first thing Hagrid does is walk up to where Harry and Ron sit, thanking them for helping prove his innocence. Harry then stands up and looks at Hagrid with a smile.
Harry: "There's no Hogwarts without you, Hagrid."
Doubly touching when you remember that to Harry, Hogwarts is the first true home he's ever had. And without Hagrid, it couldn't possibly be the same...
Completed with a big hug afterward. Professor Dumbledore is the first to applaud, but Professor McGonagalll is only two seconds behind Dumbledore to clap Hagrid's return; Madam Pomfrey is beaming with joy; Professor Sprout — the take-no-shit-when-her-school-is-in-danger teacher of Deathly Hallows — is crying with Joy! Cue the massive standing ovation from the entirety of Hogwarts!note Except Draco and his gang of friends, naturally. But the rest of Slytherin House was standing and cheering; hell, Snape was on his feet!
Could also be a tear-jerker: when everyone is clapping for Hagrid, there is a close up on Hermione who you could see is crying tears of joy at the sight of Hagrid getting the applause he deserves. This is even more heartwarming when you realize Hagrid was the one who helped Hermione get over Draco calling her a "mudblood" and she is overwhelmed with the fact that everyone realizes he is a good person.
It's a small moment, and some may disagree, but Argus Filch's reaction to seeing that his cat, Mrs. Norris, has been petrified is actually kind of heartwarming when you think about it. Filch may be unpleasant and unkind, but there's no denying he has a soft spot for his cat. His reaction to seeing her is so sad, and he's ready to kill a student when he thinks they're responsible.
Possible YMMV, but there is one scene that the movie does better than the book: In the book, Harry kills the Basilisk, is poisoned, and is then saved by Fawkes. Voldemort comments on Phoenix's healing powers before Harry destroys the diary. In the movie, Harry destroys Voldemort before Fawkes heals him; Ginny wakes up to see him still wounded. He ignores the fact that he's dying, and tries only to calm her down and get her out of the chamber safely. Because that is the kind of person Harry is.
In The Chamber of Secrets, Dumbledore told Harry, who had been doubting that he truly belonged in Gryffindor, to look at the sword he had taken from the Sorting Hat. Engraved upon it was the name Godric Gryffindor.
Dumbledore: "Only a true Gryffindor could have pulled that out of the hat, Harry."
And, when Harry admits he worried that the Hat should have put him in Slytherin:
"It is not our abilities that define us, Harry. It is our choices."
It's a small one, but the scene where Hagrid comforts Hermione after Draco Malfoy calls her a mudblood. note Note that this is a big improvement over the same scene in the book, where Hermione had never heard the term "mudblood" before that day.
Hagrid: Don't you think about it. Don't you think about it for a minute.
Made extra heartwarming, when we later find out he suffers from prejudice on both sides, for being half giant.
It's not small at all. It's a microcosm of the point of the entire series. Where we came from doesn't matter. Our choices do.
Dumbledore's reaction to Fawkes being reborn is adorable. It's basically how everyone reacts to a puppy. The cooing sounds Fawkes made just made things more heartwarming.
Minor Pet the Dog moment, but Lockhart wishing Harry luck during the dueling club was the most genuine thing he ever did.
Harry tricking Lucius Malfoy into freeing Dobby, and Dobby's reaction to his freedom:
Dobby: Master has given Dobby a sock... Master has presented Dobby with clothes! Dobby is free!
In the movie, there's the added scene of Lucius trying then to cast a spell on Harry (the killing curse, no less). Dobby, who so far had been completely afraid of him, immediately turns against his former master, sending him flying away, and makes very clear that you don't mess with Dobby's friends. Doubles as a Crowning Moment of Awesome.