I've got two links to share:

• Markup Markdown
• HTML to Markdown Converter

Both have been great. The Markup Markdown plugin could use some tweaking. Mainly, the editing window does not keep the editing toolbar in view. So, if I need something I have to go all the way back up on my screen and then all the way back down again. Mostly this is when I'm typing in a URL, because it is still easier to have the software/ editor add the code than type it in myself (I don't always catch typos in the code when I do it myself).