Google Analytics is the most user-friendly web statistics software we’ve found. We now offer a Google Analytics setup as a standard part of our website packages.
For businesses and non-profits that advertise, Google Analytics is an essential toolkit that lets marketing managers see how traffic flows to the site and what parts of the site are most effective.
Google Analytics will allow you to set goals such as sales completed or contact forms completed. It is incredibly useful to see how changes to your website improve the success rate of those goals in fine-grained detail. Google Analytics will show where users enter the site and where they fall off the path towards a completed goal.
See http://www.google.com/support/googleanalytics for more information.