On the NaNoWiMo forums, I found a post recommending this awesome site: Write Or Die.
The site is not a text editor, but it has a field where you can type. And if you stop typing for more than a few second (a range you can edit), the site reminds you to keep writing. This reminder may come in the form of gentle pop-up, an annoying sound effect, or (if you’re hard core) deleting your words before your very eyes.
Like many, I find it hard to turn off my internal editor and just put words on the page. Which makes Write or Die a great tool. For anyone else in my boat (welcome!) I can’t recommend this site enough. I expect to be using it quite a bit the rest of the month.