For years, Google has been an industry leader in providing traffic stats for your website. Google lets you use their free service, Analytics, to monitor traffic and to view a plethora of different categories of stats.
Beginning a few months ago in the fall, Google has begun to offer Real-Time stats. Google Analytics Real-Time is still in Beta, but offers a large amount of data on your visitors, as they are on your site.
Technology such as Google Analytics Real-Time can greatly help you measure marketing efforts and can allow you to spend money and time maximizing conversions instead of driving more traffic to your website like sheep.