- [p. 10/10] "'Hooray, hooray for the spinster's sister's daughter.'" In Masonic ritual there is a ritual question, to wit: "Is there no help for the Widow's Son?"
- [p. 20/19] "'They were myths and they were real,' he said loudly. 'Both a wave and a particle.'" This is a reference to the wave/particle duality theory of certain areas of physics, e.g. light, which appears to have the properties of both a wave and a particle, depending upon what context you are working in.
- [p. 21/19] "'That was where you had to walk on ricepaper wasn't it,' said Brother Watchtower conversationally." Reference to the old David Carradine TV series, Kung Fu. In one of the earliest episodes the Shaolin monk-in-training was required to walk along a sheet of ricepaper without ripping it or leaving a mark.
- [p. 29/27] "'And Bob's your uncle.'" An old British saying meaning "and that will be that". TP himself is quoted as saying it comes, "Apparently from a 19th Century Prime Minister, Lord Robert Stanley, who was a great one for nepotism. If you got a good Government job it was because "Bob's your uncle". It came to mean 'everything's all right'."
- [p. 32/30] As Carrot sets out for the Big City, his father (dezka-knik or King Ironfoundersson) gives him two things in a row: a definitively unmagical sword and then a shirt of Ramtops wool, which is known for being the kind of vest that needs hinges. More than shades here of Bilbo giving Frodo first of all a shirt of Mithril and then the Elven sword Sting which glows blueish in the presence of Orcs, from Tolkien's The Lord of the Rings.
- [p. 52/48] The fizzing and flashing illuminated sign outside Captain Vimes' office is a reference to the tired old visual cliché from most film noir. The seedy detective's office or apartment always has a big neon sign just outside the window.
- [p. 51/48] The motto of the Night Watch, "FABRICATI DIEM, PVNC", is dog Latin for "Make my day, punk". This is, of course, a well-known Clint 'Dirty Harry' Eastwood quote. The 'punk' comes from another famous Dirty Harry scene (see the annotation for p. 136/124). Notice also that the translation Fred Colon supplies ("To protect and to serve") is actually the motto of the Los Angeles Police Force. This may not be coincidental, as Terry Pratchett is on record as saying that one of his favourite authors is Joseph Wambaugh, who served in the LAPD and immortalised some of the classic policeman (and woman) types in his black comedy about the LAPD, The Choirboys. Pratchett has said that this one book was an influence on the way the Watch series developed, and students of literary influences on Pratchett are recommended to read it.
- [p. 53/49] "'The E. And the T sizzles when it rains.'" The magic tavern sign Brother Watchtower is stealing has a burnt-out 'E' and a sizzling 'T' just like the 'HOT L BALTIMORE' sign in the play of the same name.
- [p. 60/55] "'Good day! Good day! What is all of this that is going on here (in this place)?'" Carrot's actions and words in this scene are archetypal - in fact, stereotypical - of the friendly neighbourhood British bobby attempting to break up a family argument or innocent street brawl. In the sixties there was a BBC television series called Dixon of Dock Green, where every bobby was your friend and it was perfectly acceptable for a copper to walk into a room and say "'Ello! 'Ello! What's going on 'ere then?". And also, apparently, people would then stop being criminal types and apologise, rather than e.g. shoot the bobby dead. Calling people 'sunshine' (next footnote on the page), and signing off with "Evening, all" are also Dixonisms.
- [p. 64/59] "'What'd he mean, Justices?' he said to Nobby. 'There ain't no Justices.'" Cf. Death's oft-stated truism: There is no justice. There's just Me .
- [p. 76/70] "'Do real wizards leap about after a tiny spell and start chanting 'Here we go, here we go, here we go', Brother Watchtower? Hmm?'" "Here we go, here we go", sung to the tune of the Sousa march Stars and Stripes Forever, is a chant commonly associated with English football fans. It amuses British people that Sousa's rousing marches are played, without fail, at the inauguration of American presidents, as the Earwig song seems to be a favourite (Earwig-o, earwig-o, earwig-o-oh!), not to mention the Monty Python theme music, which Americans perhaps know better as The Liberty Bell.
- [p. 91/83] "It was strange, he felt, that so-called intelligent dogs, horses and dolphins never had any difficulty indicating to humans the vital news of the moment [...]" Classic mickey-take on Lassie, Flipper et al wherein mute animals could magically summon aid to e.g. trapped children by barking or jumping out of the water.
+ [p. 91/83] "And then he went out on to the streets, untarnished and unafraid." The following well-known quote: "But down these mean streets a man must go who is not himself mean, who is neither tarnished nor afraid." is from Raymond Chandler's essay The Simple Art of Murder.
- [p. 93/85] "'Who loves you, pussycat?', said Nobby under his breath." Pure TV detective Kojak. Note the use of the word 'pussycat' and his catchphrase "Who loves ya, baby?" at the same time.
- [p. 94/86] "'I've seen a horsefly [...] And I've seen a housefly. I've even seen a greenfly, but I ain't never seen a dragon fly" Reference to the 'I've never seen an elephant fly' song which the crows sing in Walt Disney's 1941 movie Dumbo.
- [p. 99/90] "'One just has to put up with the occasional total whittle.'" Describing Errol as a whittle is a typically clever Pratchettism. On the one hand 'whittle' simply means something reduced in size (usually by means of slicing bits and pieces off it), while on the other hand Sir Frank Whittle was the inventor of the modern aircraft jet engine. A nice bit of foreshadowing from TP, in the light of what Errol is to become. Whittle's university tutor in engineering is reputed to have looked over the young Frank's first tentative draft of an aero jet engine, taken a few deep reflective draws on his pipe, then patted his student kindly on the shoulder and said "Full marks for trying, but this'll never get off the ground, lad".
- [p. 103/94] "Of all the cities in all the world it could have flown into, he thought, it's flown into mine..." Obvious Bogart/Casablanca paraphrase, "in keeping with Vimes' role as the Discworld equivalent of the ultimate film noir anti-hero" (APF).
- [p. 114- [p. 118/108] "Once you've ruled out the impossible then whatever is left, however improbable, must be the truth. [...] There was also the curious incident of the orangutan in the night-time ..." Two Sherlock Holmes references for the price of one. The original quotes are "It is an old maxim of mine that when you have excluded the impossible, whatever remains, however improbable, must be the truth" from The Adventure of the Beryl Coronet, and "[...] the curious incident of the dog at nighttime" in Silver Blaze, both of which have become parts of the British language. The orangutan may also be a reference to Edgar Allan Poe's The Murders in the Rue Morgue(1841), where the brilliant detective arrives at the conclusion, through observation and logical deduction, that the murderer in question was in fact an escaped orangutan.
- [p.131/114] "Oh." She seemed deflated. "Well, if you're sure . . . I've got a lot of friends, you know. If you need any help, you've only got to say. The Duke of Sto Helit is looking for a guard captain, I'm sure. I'll write you a letter. You'll like them, they're a very nice young couple." That's allusion to Pratchet's book "Mort" in which titular character accidentally kills the duke during fight with Death and has to take his place, taking Death's daughter as his wife. - [p. 134/122] "'So I'm letting you have a place in Pseudopolis Yard.'" The Watch's second base, affectionately called 'The Yard', is a reference to Scotland Yard, where the British Police Headquarters used to be located - they have now moved to New Scotland Yard.
- [p. 136/124] "This is Lord Mountjoy Quickfang Winterforth IV, the hottest dragon in the city. It could burn your head clean off." Vimes replays here one of the best-known scenes in Clint Eastwood's first 'Dirty Harry' movie, 1971's Dirty Harry itself. "Aha! I know what you're thinking... Did I fire six shots or only five? To tell you the truth, I forgot it myself in all this excitement. This here's a .44 Magnum, the most powerful handgun in the world, and it can blow your head clean off. Now, you must ask yourself one question: "Do I feel lucky?" Well, do you, punk?" Note how nicely Winterforth the fourth corresponds to the caliber of the Magnum.
- [p. 143/130] "E's plain clothes, ma'am,' said Nobby smartly. 'Special Ape Services'." Special Ape Services shares the acronym SAS with the crack British special forces troops.
- [p. 162/147] "[...] and stepped out into the naked city." The Naked City was an American TV cop show in the 50s mainly remembered for its prologue: "There are eight million stories in the naked city. This is one of them." This phrase is also used by Vimes when he wonders why, out of all the million stories in the naked city, he has to listen to grubby little ones. This is when Colon tells him about the Ankh-Morpork Fine Art Appreciation Society ("hem hem") on p. 195/177
- [p. 200/182] "'He's called Rex Vivat.'" Rex Vivat, of course, means: "long live the king", which Sham has seen printed on the mugs and teatowels.
- [p. 241/219] "Someone out there was going to find out that their worst nightmare was a maddened Librarian. With a badge." The movie 48 Hrs, starring Nick Nolte and Eddy Murphy, has a scene in which Eddy Murphy is in a bar full of redneck Americans, shouting "I am your worst nightmare! A nigger with a badge!"
- [p. 278/252] "'All for one!' [...] 'All for one what?' said Nobby." "All for one and one for all" was of course the motto of the Three Musketeers, made famous by Alexandre Dumas.
- [p. 314/285] "'Here's looking at you, kid,' he said." Yet another quote from Casablanca, keeping up the Vimes-Bogart link.
Dubious folk-singer Rambling Syd Rumpo (Kenneth Williams) effectively invented the "zero entendre", where a made-up word with no meaning at all was manipulated into sounding as if it were something horrendous or filthy. Sung in an all-purpose Borsetshire English rural accent, his songs conveyed meaning out of nothing. Imagine the following, sung to the tune of Clementine-
"So they hung him by the postern, Nailed his moulies to the fence; For to warn all young cordwanglers That it was a grave offence" (Ballad of the Woggler's Moulie)
Some of Syd's Memorable songs
None of these would be out of place in Ankh-Morpork, where they sing Where Has All the Custard Gone?
- The Ballad of the Somerset Nog (to the tune of Widecombe Fair) 
- D'Ye Ken Jim Pubes (to the tune of D'Ye Ken John Peel)
- Green Grow My Nadgers O! (to the tune of Green Grow The Rushes-O) 
- The Ballad of the Woggler's Moulie (to the tune of Clementine)
- The Taddle Gropers' Dance (to the tune of Here We Go Round The Mulberry Bush)
- What Shall We Do With The Drunken Nurker 
- 'Twas On The Good Ship Habakkuk
- Clacton Bogle Picker's Lament
- Runcorn Splod Cobbler's Song 
- Granny Went a-Wandering
- Song Of The Australian Outlaw 
- The Black Grunger of Hounslow 
- Gladys Is At It Again
- The Song Of The Bogle Clencher
- The Grommet Tinker's Song
- My Grussett Lies a Fallowing-oh
- Bind my Plooms with Silage
- The Russet-banger Ditty
- The Lung-Wormer's Gavotte
- Good King Boroslav
Carrot Ironfoundersson: the musical
Discovered in complete serendipity, I'm really surprised nobody else has found this. Offenbach's 19th century light opera Le roi Carrotte (King Carrot), in which a humble Carrot first becomes human, and then becomes King, deposing a hated tyrant in the process...
See here:- 
And there's also the serious musical version, the sort that lasts for three days straight and involves large ladies wearing horned helmets, strategically placed dustbin lids sprayed gold, who wave spears. A human of heroic proportion, but naive? A foundling brought up by dwarfs, off to make his way in the world? Knows no fear? About to encounter dragons? Siegfried from Richard Wagner's Ring Cycle, perhaps?