Many good answers on this site are going to require quoting passages of the text of a novel, poem, play, or other piece of literature. Thus, knowing where to find such passages is going to be very important for the site's users in composing their answers.
Copying them out by hand from paper books works, but is slow and tiring. Finding pirated texts online probably also works (I've never tried), but we don't want to encourage that here. So:
what are some good, legal, online resources for finding texts to quote?
I'll post a community-wiki answer to this question which anyone can edit. Let's try to get a really good list all in one place so that we can refer people to it in the future.