The other day a great comment was left on this site. When I went to answer, I realized that I wanted to be able to select part of what the commentator said and automatically turn it into a quote in my comment.
Copy and paste are too mundane for me, so I wrote a Greasemonkey script that adds the markItUp! Editor to any textarea on a page. I then extended markItUp! by adding a ‘quote’ button that wraps the currently selected text (from anywhere on the page) in blockquote tags.