[Toraspanda]

One line that always amuses me, but it's only in the film, is spoken by one of my least favourite characters, Ron. When Hermione accidentally turns herself into a part cat, and wails "Look at my face!" - and Ron counters, "Look at your tail!"

In the book of course (Chamber of secrets) Ron only says "Uh-oh", and it's Moaning Myrtle who chortles, "Wait till they find out you've got a tail!" - a rare case of a film improving on the book!

I also loved Molly Weasley's "Not my daughter..." during the Battle, and Dumbledore's "few words" at the welcoming banquet in The Philsopher's Stone:
"Before we begin our banquet, I would like to say a few words. And here they are: Nitwit! Blubber! Oddment! Tweak!"