The web is all about sharing information. The things you received for free you should spread for free. This excellent web statistics package falls in that category. 

Some time ago, Google bought Urchin web analytics software. It allowed you to track number of visitors, from what search engines and keywords, and so much more. From what I understand, Urchin used to cost upwards of $500/mo. Google aquires it, improves it, and releases it for free. It is a snap to install on any website, not taking any more than 15 minutes for your webmaster to put on there.

Learn more about Google Analytics here.