http://www.nanowrimo.org/ . FYI- the site sometimes get overloaded on the first day.
What is NaNoWriMo? It is 30 days and nights of literary abandon! Basically, you write a 50,000 word novel and you only have November to do it in.
Why do it? Have you been waiting for that kick in the pants? Here it is. Join thousands of others in a collective effort, get daily writing support and encouragement, accomplish an amazing feat.
Don't know where to start? Check out this great blog about choosing the right story from Nathan Bransford from NaNoWriMo Boot Camp 2010- http://blog.nathanbransford.com/2010/10/nanowrimo-boot-camp-choosing-right-idea.html