Most of my clients already know about this… but just to be sure…
Currently the “gold standard” for Web analytics services is Google Analytics.
This extremely powerful Web-based statistics package used to cost $400/month before Google bought it and now makes it available to anyone for free — that’s right, no cost whatsoever.
Just go to https://www.google.com/analytics and sign up for your free account. Once signed up, your Webmaster will need to install a small snippet of code on every page of your site that you want to track.
After that, you will be able to log into your Google Analytics account from any Web browser and see up-to-the-minute real time statistics on everything you could ever want to know about your site visitors and their behavior.