National Novel Writing Month

Even though the month of November is almost over, this site has a great challenge that could be used at any time for an English teacher. There are two sites, but they both have the same goal in mind, write the majority of a novel (50,000 words) in one month.
The first is the National Novel Writing Month also known as "NaNoWriMo".They provide you inspiration with help hints, forums to ask questions, and a Young Writers Program as well.
The Young Writers Program has a similar site as well but with it geared towards teenagers instead. They have games and suggestions on how to get rid of writers block.
This would be ambitious for any teacher to have their students write this much, but they could easily adapt this exercise across a semester or year.