I have to admit this is not designed for Oscommerce, but it is the best contribution I have installed on my Oscommerce, I take no credit as it is designed by a friend of mine...
phpMyVisites is a free and powerful open source application for websites statistics and audience measurements.
phpMyVisites gives a lot of information on websites visitors, visited pages, software/hardware utilization, etc... The GUI Interface is fun and practical. The installation is entirely automated and the possibilities of configuration are extensive and automated also.
You can find out more about it and download it at www.phpmyvisites.net
Sorry if this is not considered as a contribution, but it is a really good tool to have and use with Oscommerce
For instalation with Oscommerce, just paste the code that is generated into the index.php if you are using a template contribution, you might want to paste the code into the index.php template file...
And of course, this system can be used for your non commercial websites.