Alexa has a tool bar and search engine that a lot of people use. Alexa uses their tool bar and search engine like Neilsen uses the little box in the television set - to check what sites people go to. Alexa publishes these data as rankings of Web sites and viewers per million. See www.alexa.com for more info.
You can also compare relative rank of sites: www.developers.evrsoft.com/find-traffic-rank.shtml
Check it out.