Google Analytics is now free, you can track stats for multiple sites (profiles) from a single Google Analytics account, the sites you wish to log traffic on does not have to be on the same domain as the one you registered your account with.
To log traffic couldn't be simpler, you are given a snippet of javascript to add to the web page that you want to collect statistics from.
See a screenshot below for one of the traffic stats page for my GWB blog.
For quick access to your site's stats you can use Google analytics module to display Google Analytic Stats on your Google Homepage.
