There is a tutorial on how to create a burndown chart for Scrum in the Google Docs application:

http://www.scrumology.net/2011/05/03/how-to-create-a-burndown-chart-in-google-docs/

The problem I see with it though is, it has only a place to update progress once per sprint but the burndown is supposed to be updated with daily progress, right? How can one modify this chart to be able to put daily progress on it?