Wyrd Sisters - Granny Weatherwax attending her first play
The Light Fantastic (I think) - the wizards summoning Death (I hope you know I was at a party...)
Pyramids - the "namby pamby saying his prayers" scene at the Assassins' School where the namby pamby is drawing a pentacle and sacrificing a goat
Moving Pictures - the reverse King Kong scene with the giant woman carrying the Librarian up the Tower of Art
Making Money - the clown scene near the end
Unseen Academicals - the orc analysing himself
Mort - Death in the conga line. Death's interview at the employment office
Hogfather - The scene in the department store of course! Has already been mentioned but fantastic...
Small Gods - The Ephebian philosophers in the tavern
Guards! Guards! - The scene with the doors in the rain and the secret passwords near the beginning
Going Postal - the scene ending with the letters saying "Deliver Us" (worst Pratchett pun ever perhaps?)
. The pin collecting shop (nicely done in the TV version too)
Monstrous Regiment - everything to do with socks
Enough for now...