In the Facebook world, today is Harry Potter Status Day, commemorating the defeat of Lord Voldemort, and users are supposed to post HP quotes as status updates. If you don't have a favorite, there are websites to help:
Listfied offers dozens, including Dumbledore's "Happiness can be found, even in the darkest of times, if one only remembers to turn on the light," and Harry's "I don't go looking for trouble. Trouble usually finds me."
You can find many more at Mugglenet ("You know your mother, Malfoy? The expression on her face - like she's got dung under her nose? Is she like that all the time or just because you were with her?" -- Harry) and The Quote Garden ("Never trust anything that can think for itself if you can't see where it keeps its brain." -- Arthur Weasley)