There are a number of different paid and free tools available to track web traffic and web related trends. I have used a number of them and many of them have their strengths and weaknesses. The choice/s of your selected web analytics software depends on the purpose of your website and how these tools help you optimize the visitors' experience on your sites.
For a small website, perhaps Google Analytics or Yahoo Analytics is best. What have been your experience using such tools? I have also used fee based web analytics tools like WebTrends and Urchin.
So the most important question is, what do you do with the web traffic data? Do you read the reports consistently or once in a quarter?