The giddy hug between Tom, Gwen, and Sybil in the first season finale. Made even better if one notices Tom and Sybil hold hands after the three break apart.
It's a small moment, but this troper was very touched when Cora secretly watches Sybil bake her first cake. The smile on her face just makes the scene.
Another small Sybil-related moment: Tom peeking in the window to see her harem-pants dress, and the adorable, boyish grin he can't hold back.
Bates and Anna, at the table, discussing their future together. When he reveals all his hopes and dreams for their future so thoroughly planned, it settles the argument once and for all that yes, he is just as deeply committed to her as she is to him.
"Miss Swire... as if any man in his right mind could prefer Miss Swire to you." And with that, Carson, you've become my favorite for all time.
Mrs. Patmore, shown previously to be a bit prickly, discovers Mrs. Bird running a soup kitchen in secret, instantly drops everything and helps cook and keep it a secret.
Matthew and William returning home during the concert after being reported missing. The looks he and Mary share could melt glaciers.
Even more of an heartwarming moment when Matthew goes all protective on her with his indirect If You Ever Do Anything to Hurt Her... to Richard Carlisle, telling her that if Richard ever did hurt her, he'd be obliged to step in. Compounded with the fact that he always carries around her lucky charm when in the combat zone (and not, say, Lavinia's photo), this tells the audience that he still very much cares about her...
Edith getting her moment in the spotlight when the entire dinner table guests turn to thank her for her efforts to help the convalescing officers at Downton.
General Sir Herbert Strutt: I also think we are forgetting someone here... the officers tell me of someone who has been a great help to them.
General Sir Herbert Strutt: Here. Lady Edith.
Keep in mind that when the exchange begins, Cora and Isobel look expectant, because both have been in a rivalry over running the hospital and both are hoping that they will be named as the most helpful. Edith, meanwhile, did everything for the injured soldiers out of a genuine desire to help them be more comfortable.
The entire story that Carson tells of four-year-old Mary in Episode 7 of Season 2.
Matthew and Molesley coming to a quiet, unstated mutual agreement during the second episode of series 1 when Matthew lets Molesley really do his job for the first time.
"You are a lady to me. And I never knew a finer one." Oh, Bates.
Ditto "I think I would love you however, whatever, whenever..."
Also on the subject of Bates and Anna: "I would marry you now if I weren't already your wife!" Oh, Anna!
Robert finally giving his blessing to Sybil and Branson.
The entirety of Carson and Hughes' relationship.
Throughout the series, Mary has been afraid of what her father will do if he ever finds out about the truth about Mr. Pamuk. When he does find out, and also discovers that the threat of exposure is why Mary still wants to go through with her marriage to Sir Richard, his reaction is immediate: "I don't want you spending your whole life being unhappy because of the threat of scandal. Break it off with him. Go to America to wait out the storm, visit your Aunt and come back with some rich young buck to shake us up!" Cue the father-daughter hug. D'awww.
Similarly, Matthew's reaction when Mary tells him about Mr. Pamuk. He is shaken, but the first thing he tells her is "I could never despise you" (this being in response to her saying that he would despise her if he ever learned her secret). She then asks if he's forgiven her for it, and he replies that he has not...because she's done nothing that needs forgiving. He then proposes and she accepts. After two seasons, they finally are engaged! Daw!
When Matthew sees that Mary is unhappy with Sir Richard, he tells her that she shouldn't feel the need to marry simply to secure her own future, saying "You'll always have a home here, as long as I'm alive."
William's father informally but very earnestly adopting Daisy as his own and then giving her advice about her future. Definitely a Tear Jerker as well, but also very heartwarming.
The damn near giddy look on Mrs Hughes' face as she watches Carson polishing silver whilst humming "She Stole My Heart Away" after learning that she's cancer-free. She bites her lip and beams like a schoolgirl. God, those two.
The immediate reaction to Edith being left at the altar from damn near everyone: rallying around her, offering comfort. Even Carson permits some bad words to be said about Sir Anthony....but only just this once.
On learning that he's been declared a "dangerous prisoner", Bates is confused and not particularly interested... until he learns it means they've stopped his letters and visitors, at which point he's very nearly giddy. Because it means that Anna hasn't given up on him.
Bates being set free and his reunion with Anna. Considering what this show likes to do to the both of them, chances are it won't last long.
The normally self-serving Thomas telling Carson that Jimmy didn't reciprocate his affections or his kiss. Keep in mind that being homosexual was illegal in Britain at the time, and if Jimmy decides to report Thomas to the police, all the punishment will be on his head.
Bonus points for the finale, where Lord Grantham, Bates and Carson defend Thomas to protect him and Downton from controversy, despite the common view on gays:
Robert: I'm not asking you to abandon your beliefs, Alfred. Just to introduce a little kindness into the equation. Alfred: Am I not to stand up against evil? Robert: Evil? Thomas does not choose to be the way he is. And what harm was done, really, that his life should be destroyed for it? Alfred: Well— Robert: Let he who is without sin cast the first stone. Are you without sin, Alfred? As I am certainly not.
In general, the way almost everyone stands by Thomas despite his obnoxious personality, right when he expects their disgust.
The final scene of season 3, episode 8: Robert, Tom, and Matthew laughing together as they play cricket. Made even more heartwarming by the thought that this is what Sybil wanted: to see Tom and her family get along.
Just before that final shot of Robert with his sons-in-law, the moment where Matthew and Mary are holding baby Sybil and Tom affectionately pats them each on the shoulder before a heartwarming conversation with Cora about staying at Downton.
Pretty much any of Matthew and Mary's conversations in bed in Season 3. Really, every single one is so adorable it's impossible to list them all.
In the 2012 Christmas Special, while at the fair, Jimmy gets drunk and runs into some trouble with two thugs underneath a bridge. Then, out of nowhere, comes Thomas to save him. Thomas gets beat up pretty badly, but afterward, Jimmy visits him and tells him that he was brave. They have a nice little talk, Thomas asks if they could be friends, and then they share a newspaper. It's a cute, quiet moment (and potential Ship Tease?) that shows Jimmy's willingness to forgive Thomas for creeping on him and also shows Thomas' apparent desire to be a nicer person.
Again from the 2012 Christmas Special, there is Mary giving birth to a healthy boy. Matthew and her share an especial tender moment as he holds his son for the first time.
Another from the special is Carson refusing to go to the Thirsk Fair with the rest of the staff. Not because he doesn't want to, but because him being there would mean everyone would be too nervous to let loose and have fun. And while everyone is away, what does he do? He spends the day with little Miss Sybil, carrying her around the house in the same way he most likely carried her late mother. D'awww
A minor one from the Special: after their less-than-stellar beginning, it's nice to see Daisy and Ivy have become best friends.
The identical looks of parental pride on their faces when Carson and Robert see Mary in her wedding dress.
The reveal at the end of the series 3 premiere that Violet was the one who sent Sybil and Branson tickets so they could attend Mary and Matthew's wedding.
Cora telling Mrs. Hughes that if she does turn out to have cancer, she can stay at the house and the whole family will take care of her (which is something that really couldn't be counted on at the time).
Cora: Mrs. Hughes, I only want to say one thing: that if you are ill, you are welcome here for as long as you want to stay. Lady Sybil will help us to find a suitable nurse... I don't want you to have any concerns about where you'll go or who will look after you, because the answer is here, and we will.
Similarly, Robert sending Mrs Patmore to have her cataracts treated at one of the best hospitals
After Sir Anthony calls out the jerk that drugged Tom's drink, Matthew shows his solidarity, as he said earlier in the episode, by asking him to be his best man.
Speaking of Tom and Matthew, how about when Tom goes to talk to Matthew after he and Mary fight the day before their wedding?
And then when Matthew goes to talk to Mary. And then the horrifically romantic kiss where they close their eyes (it's bad luck for the groom to see the bride) an step around the door... only in so florid a period as the Edwardian could something so overwrought possibly be realistic. And wonderful.
When Edith's letter appears in the paper, the identical looks of brotherly pride on Tom's and Matthew's faces.
When Cora goes down to the kitchen to scold the servants for some shady business, but when she learns they are feeding starving soldiers, she volunteers to help.
Mr. Carson holds Sybil's baby and starts cooing to her. She stops crying and warms up to him immediately. As if that wasn't enough to melt you right there, the old softy then goes on to reminisce to Mrs. Hughes how he held Sybil when she was that small.
It's a small one, but the tug-of-war game in the 2012 Christmas special. After the Downton team wins, the boys (Alfred, Jimmy, Tom, and Thomas) collapse in a tangle on the ground, laughing together like the young men they are. Then Tom reaches down to give Thomas a hand getting up and they hug in the background. Possibly informed by the actors' real-life friendship, but still a nice moment to show that Thomas, whatever his faults, does have friends, and that Tom, even though he's married into the family, still enjoys having fun with his former colleagues.
There's also the scene after, where Thomas saves Jimmy from some men he hustled, even though it means Thomas is severely beaten up. When they meet after, Jimmy thanks Thomas, but says that he's afraid they can't have the sort of relationship Thomas wants. Thomas asks if they can just be friends then, which Jimmy agrees to. The scene ends as Jimmy pulls up a chair and reads to Thomas from the newspaper.
Anna surprising Mr. Bates and Mary by showing off how she'd been taking dancing lessons in secret. Mary, impressed, comments on how extraordinary Anna is. Mr. Bates agrees, while looking at Anna with such a look of pride and love. It's so incredibly sweet!
Although the Season 4 premiere is suitably grim following Matthew's death, there are a few moments that warm the heart:
Carson holding Mary as she sobs over losing Matthew, just as he did way back in Season 1
Tom spending much of the episode being a protective brother to Mary, culminating with literally giving her a seat at the table to discuss the estate.
Really, you can see the evolution of Tom and Mary's relationship in one scene. Edith, Cora and Rose are talking eagerly about Edith's trip to London, while Mary is sitting in the corner. Tom approaches her and gently tells her to find something to do in the wake of Matthew's death. He knows what's she going through better than most. It's the only real conversation Mary engages in before the end of the episode, when she finally starts to come out of her mourning.
Thomas and Sybbie. After the events of Season 3, he seems to have softened a little, and nowhere is this more evident than his affectionate address to this little girl (who he calls a "friend"), who smiles happily up at him. It appears we may have the makings of Carson and Mary in a new generation.
Mrs. Hughes helping Mrs. Patmore clean up the broken bowl from the electric mixer after Mrs. Patmore reveals she's afraid all the new appliances will make her unnecessary, saying it makes Daisy look like part of the future and it leaves her stuck in the past.
Violet's entire conversation with Mary, culminating in her saying that she loves her. This is the first time ever that Violet has ever said these words onscreen to anyone in her family.
It's subtle, but when Mary enters the boardroom at the end, she's wearing the colour violet.
Despite the insensitive comment earlier on in series four, the Duchess was trying to cheer Branson up. She recognized the pain one feels in losing their significant other. Made more apparent in the fourth episode when she explains how when the Duke died, she felt lost and couldn't do anything anymore. Branson points out that she could, to which she replies that he will be able to to.
Isobel Crawley shaking Anthony Foyle's hand in 4.04. It's significant and an especially kind-hearted gesture from her since it's implied that he might become Mary's second husband following her son Matthew's death. Violet's praise of her afterwards should be heard to be believed.
In 4x05, Mary's genuine smile and affectionate greeting upon the return of Evelyn Napier.
Isobel, Mary and Tom sitting in the nursery and reflecting on how happy they were when they were about to marry their spouses: Reginald Crawley, Matthew and Sybil respectively. Topped off with Isobel smiling brightly and saying "Well, aren't we the lucky ones?"
Isobel nursing Violet (who has never cared for her) back to health when she contracts bronchitis for two days straight without sleeping, eating, or drinking. Violet is so ill she doesn't know it was Isobel until Dr Clarkson tells her that "there was no other nurse."
Jack Ross, a black jazz singer, strikes up a romantic relationship with the white Lady Rose, but soon realizes that because of the prejudices common in the 1920s, such a romance would be unwise and even dangerous for the both of them, so he tells Lady Mary, who comes to talk him out of being with Rose, that he has decided on his own to end the relationship. As Lady Mary leaves, they have this exchange:
Jack: If we lived in even a slightly better world, I wouldn't give in.
Mary: It may surprise you, Mr. Ross, but if we lived in a better world, I wouldn't want you to.
Despite having the opportunity to destroy Matthew's engagement to Lavinia (and even being encouraged to do so by her aunt and grandmother), Mary instead welcomes her. No matter how much she might be in love with Matthew herself, she wants him to be happy, even if it's not with her. This is quite a change from her ruthless characterization in season one.