There's also Googleanalytics. There are many tools on it. Am still learning the ropes but the default tools have wowed me. It tells us how many visitors, from where, and how they came to the site and how long they stayed and what pages they visited for how many times and how many were unique visitors and how many were returning ones.
It also allows us to test out content and how effective it is in converting visitors to customers. That one I have yet to try out.