“Using a metaphor in front of a man as unimaginative as Ridcully was like a red flag to a bu-- was like putting something very annoying in front of someone who was annoyed by it.”
“He married that Palliard girl, remember? The one with the air-cooled teeth?”
– (Terry Pratchett, Lords and Ladies)
What are your favorites?
QtM
“Give a man a fire, and he’s warm for a day.
Set a man on fire, and he’s warm for the rest of his life.”
Jingo
In Ghat they believe in vampire watermelons, although folklore is silent about what they believe about vampire watermelons. Possibly they suck back. (Carpe Jugulum)
“Go on, do Deformed Rabbit… it’s my favourite.” (Small Gods)
The gods of the Disc have never bothered much about judging the souls of the dead, and so people only go to hell if that’s where they believe, in their deepest heart, that they deserve to go. Which they won’t do if they don’t know about it. This explains why it is so important to shoot missionaries on sight.
– (Terry Pratchett, Eric)
The three rules of the Librarians of Time and Space are: 1) Silence; 2) Books must be returned no later than the date last shown; and 3) Do not interfere with the nature of causality.
– (Terry Pratchett, Guards! Guards!)
You can get more Pratchett quotes here.
“Rincewind could scream for mercy in nineteen languages, and just scream in another forty-four.”
Interesting Times
“Thunder rolled…It rolled a six.”
Guards! Guards!
I’ll have to scan my Pratchett library when I get home from work.
Also, see my sig. 
Nice “sig”, Atreyu.
What our ancestors would really be thinking, if they were alive today, is: “Why is it so dark in here?”
– (Terry Pratchett, Pyramids)
Rats. I keep forgetting that I have to click on that little box a second time after previewing the response.
“When you hear someone shouting “Onward, brave comrades!” he’s usually the one behind the rock wearing an arrowproof helmet!”
– Rincewind, Interesting Times
“Just because it’s not nice doesn’t mean it’s not miraculous”
Interesting Times
“When you really need them the most, million-to-one chances always pop up. Well-known fact”
Sergeant Colon, Guards! Guards!
“People who are rather more than six feet tall and almost as wide across at the shoulders often have uneventful journeys. People jump out at them from behind rocks and then say things like, ‘Oh. Sorry. I thought you were someone else’.”
Guards! Guards!
Ipslore: “What would humans be without love?”
Death: RARE.
Sourcery
there are so many, many more, but I think this is enough for now.
Would it be tasteless of me to point out that I’ve got a massive collection of Pratchett quotes on my web site? Complete with search engine, no less.
http://www.digiserve.com/eescape/closet/Closet.html#Pratchett
(I can’t even begin to pick a favorite, are you kidding? ;))
The only things known to go faster than ordinary light is monarchy, according to the philosopher Ly Tin Weedle. He reasoned like this: you can’t have more than one king, and tradition demands that there is no gap between kings, so when a king dies the succession must therefore pass to the heir instantaneously. Presumably, he said, there must be some elementary particles – kingons, or possibly queons – that do this job, but of course succession sometimes fails if, in mid-flight, they strike an anti-particle, or republicon. His ambitious plans to use his discovery to send messages, involving the careful torturing of a small king in order to modulate the signal, were never fully expanded because, at that point, the bar closed.
(from Mort)
And the sig, of course.