Signing up to Google Analytics - Monitor your traffic

http://www.google.com/analytics/

All you have to do is sign up with your google email account and you will get code to add onto your website, paste the code at the bottom of the page, just before the </html>

Then you can login to google analytics and see all the stats daily. You will be able to check refering sites, bounce rate, average time on site, pageviews, and visitors. (You can monitor what countries your visitors come from.)

Their are plenty more uses such as warnings if you have the same page description on every page. The best function on there by far for me, is the automatic email function, so all of our customers can get an email monthly with a PDF of our stats, this proves our stats, as we have no way of editing the PDF.