Erik Benson's spreadsheet is terrific.
"The NaNo Report Card works by taking the total word count for your novel and the number of hours spent writing each day, and giving you back a slew of charts, graphs, and colorful numbers about how much you've written today versus yesterday, and the number of words per hour, percent complete, and estimated complete date. It also sets word count goals that you can use to hit a Nov. 30 completion date. Missing a day of writing doesn't seem as futile because the spreadsheet will tell you that you just need to write a little more each day rather than try to write twice as much tomorrow. I think it helps prevent your brain from declaring doom too early. "
Here's the link. When you get to the page, scroll down until you see Erik Benson's question, and you'll find the download link.