Some offers I noticed while I was over checking out the NaNoWriMo website:
You can use Pangurad "free during NaNoWriMo 2011. PangurPad is a new kind of online writing tool and publishing system with many features and a fantastic community. As an official NaNoWriMo 2011 participant you can use PangurPad entirely free of charge to write your novel, then format and embed it directly on your website or publish it as an eBook. Any participant signing up for a full membership before December 31st will be supporting NaNoWriMo with 5% donated back to the Office of Letters and Light." Nice that they give back a bit to the NaNo folks.
Yarny promises always to have a free version online (which is why I already love them) that allows you to "Write the way you want to write, using any approach you like in a simple, distraction-free environment. It's novel writing in the cloud. In today's world, we just don't think you should have to learn to use software anymore. With automatic saving, versioning and simple ways to track the people, places and things in your novel, it's easy to get organized and stay focused. We will always have a free version. A few things won't be free, but not many. Paid plans, beginning in December, will be dirt cheap. And, all NaNoWriMo winners get 50% off of an annual subscription."
WriteWay has a demo version you can use for free until 12/15/11, and is also offering a 50% discount on their Pro version; see more details at their NaNoWriMo page here.
Finally, to do my part to contribute a freebie for NaNoWriMo, from now until December 1st you can get a copy of my out of print writing how-to, Way of the Cheetah in .pdf format. Read online, download and/or print out the e-book here.