Google Analytics is a free tool by Google that allows to use track information about visitors to your web site as well results to your e-marketing campaigns. As Alicia Whalen, A Couple of Chicks E-Marketing, states the web is the best medium to track marketing results.

Google Analytics provides one of the most comprehensive reports on your web site that provides information on visitors, content, goals and so much more. This tool provides an executive summary 4-5 pages in pdf form or you can print the whole report out 39-45 pages or just view it.

Once you setup an account, an e-mail address with Google, you are eligible to use Google Analytics.
Google provides an excellent installation guide for you as well a blog to keep you updated. Below are posts and or articles from various blogs on Google Analytics:

1) Google Analytics gets a Facelift
2) Google Analytics - Best Choice for Web Stats
3) Google Adwords & Analytics - an email leads to a couple of tips
4) Google Analytics - A Must Have Tool for your Web Site
5) Reminder: Google Analytics to complete transition to new interface on July 18th