Heartwarming / Feet of Clay

• Detritus and Cheery. If you've read Men at Arms, you already know that one of Detritus's first friends was a dwarf that overcame centuries of cultural prejudice to accept him as a friend and comrade-in-arms. Now, Detritus is returning the favor to befriend and defend Cheery.
• One of Vetinari's rare moments of visible emotion, after Vimes told that the religious leaders want to destroy Dorfl.
  'I've given that viewpoint a lot of thought, sir, and reached the following conclusion: arseholes to the lot of 'em, sir.'
  
  The Patrician's hand covered his mouth for a moment.
• Angua's story about Mrs. Gammage at Biers. Mrs. Gammage is an old lady who has been drinking at the undead bar since before it was the undead bar, and never noticed the change. She was robbed once. The stolen goods were returned the next day and the thieves discovered to be mysteriously empty of blood.
  • Also the fact that Mrs. Gammage is clearly senile, and believes everyone in the bar to be one old friend of hers or another - and everyone plays along rather than upset her with the truth.
• At one point in the story, Vetinari poses a Who Watches the Watchmen? question to Vimes. Vimes' answer is simply "We watch each other."
• Dorfl recollecting Carrot's honest kindness and fighting even harder against the king when he notices Carrot later on in the book is definitely a topper.
• Why did Dorfl return from 'death'? WORDS IN THE HEART CAN NOT BE TAKEN
• When Vimes points out that the golems could win their freedom by violent revolt - "Not that I'm advising that in any way, of course" - Dorfl spurns the idea in the humblest possible way:
  No. That Would Be Wrong. We Will Be Freed By Our Own Hands, Or By None.
• Cheri spends most of the book with major prejudice against werewolves, not having any idea that Angua is the Watch's werewolf. When she does learn that Angua is the werewolf, after she changed to save Cheri's life, nothing changes between them.
• While it's framed via Angua's worry for Carrot, there are a couple of lines which speak volumes of Carrot and Vimes.
  "Commander Vimes said someone has to speak for the people with no voices!"
  He really believes it, Angua thought. Vimes put words in his head.
• Dorfl's intro scene (before it's established who he is) has him trying to save the old priest who helped the golems from dying through the only way he knows: writing the same words that are on his chem on a piece of paper and putting it in the old man's mouth. It obviously doesn't work, but the priest realises what he's trying to do and seems genuinely appreciative.
• Vetinari admitting to Drumknott that part of the reason he let things go on as long as he did was that "Vimes was having so much fun."
• Why doesn't Nobby want to be king? Because Vimes wouldn't like it. Becomes even more heartwarming after Night Watch, when we learn (though Nobby didn't) that Vimes was kind to him as a child.
• After Mildred Easy realizes that she's partly responsible for the deaths of her grandmother and her little brother, Vimes comforts her by promising that she won't lose her job, and that she's welcome to the Watch House's used candle ends if she needs them.
• When Dorfl is inducted as a Watchman, Vimes gives him a chit of paper to show anyone who denies that he is a person. Dorfl solemnly says that if he ever feels that he is not alive, he will look at it.