How to get more info on who is visiting your site

In addition to any on-site web analytics tracking that you might do using Google Analytics, Coremetrics, Omniture, or other solutions, there are a number of vendors who use other methods to provide information about who is visiting your website.

Recently Robert Scoble at Fastcompany TV sat down with the CEO of yet one more vendor, Quantcast. Check out their interviews here: Quantcast Part 1, Quantcast Part 2