Google Analytics tells you everything you want to know about how your visitors found you and how they interact with your site. You'll be able to focus your marketing resources on campaigns and initiatives that deliver ROI, and improve your site to convert more visitors.

Integrated with Adwords.
Google Analytics has the enterprise level capabilities you'd expect from a high end web analytics offering and also provides timesaving integration with AdWords. Of course, Google Analytics tracks all of your non-AdWords initiatives as well.