Quantcast.com

http://www.quantcast.com is a page that estimates information about a Web site, including traffic frequency. I am not expert enough to know if these estimates are close to reality, but they seem plausible.

There are similar Web sites (for example, WebSiteShadow.com) that try to do even more, but from looking at their results on academic institutions I am familiar with, I can tell that they are inaccurate.

_-D.D.