ZdStats is a wordpress plugin allowing you to trace your visitors. This is not a simple statistics plugin, it’s very flexible and dynamic. This means you can update your filters by yourself and therefore by as realistic as possible.
Here is a lsit of functions :
* Display a summary of visits (week, month, trimester, semester and year)
* Display Pageviews and visitors with daily precision
* Referring pages
* Used keywords
* Localization of your visitors
* Browser / OS
You can grab it here and read documentation here
Anthony.