Write or Die is a web application that encourages writing by punishing the tendency to avoid writing. Start typing in the box. As long as you keep typing, you're fine, but once you stop typing, you have a grace period of a certain number of seconds and then there are consequences.
Want to write a novel in a month? NaNoWriMo is a great tool for those creative writers out there, but also useful for non-fiction writers as it allows you to easily track your word count.