An HTML to Markdown converter written in javascript.
A basic implementation is there, but it's not yet fully bulletproof (contributions welcome!).
There are a couple of known issues surrounding blockquotes in lists (and perhaps vice versa) — #2; and also how to handle HTML elements outside of the markdown subset (keep them/strip them?) — #3.
to-markdown is copyright © 2011 Dom Christie and released under the MIT license.