Generally in online world we need to look for some website’s reputation and traffic estimation for general analysis! I already know there are some online tools or Websites e.g. Compete, Alexa, Quantcast etc.
I request you all people to provide me some of the good free online tools for estimating website traffic!
I haven’t heard of any outside of Alexa. The pagerank of the site may give you some indication as its popularity too.
that’s pretty sad that You haven’t heard anything out of Alexa but compete and quantcast are also the good ones for showing the website traffic ,the only limitation with these tools is that they provide limited sad of data! 
The Page Rank can’t help in any relation with the traffic because Page Rank is just a part of the Search engine Google’s Ranking Algorithm !
you may try one of these ways:
SEMRush tools- it will help you to track rank of keywords
Google tools
[FONT=verdana]Adrian, you asked about tools for estimating traffic. I don’t know about that, but there are plenty of tools available that will tell you your actual traffic.
Many web hosting packages come with utilities such as AWStats or Webalyzer. These are easy to use. You just need to enable the product in question, and it will give you a detailed report of your traffic. Or, you can choose a product like Google Analytics or StatCounter. In those cases, you get much more detailed information, but you will need to add some code to every page on your site.
If that doesn’t answer your question, perhaps you could clarify what you’re looking for.
Mike
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Mike, I suspect the OP is looking to understand someone else’s site traffic.
Unfortunately this is still a very limited science given the attonomy between sites [dns aside there’s no centralization for website visits] thus to measure an external site is really about sampling from an isp or having enough click data to draw a sample from. The smaller the site the less you’ll know and the less accurate it is.
You’ve already listed the major low-end tools, compete being the commonly used but there are others on the enterprise end including Hitwise [ISP info], comScore and Nielsen Netratings [audience groups]. As you’d suspect these can be much more accurate but only tend to work for sites > 1mm uniques ideally and from what I’ve been told perhaps 500k as a baseline. And they don’t come cheap, but then again good data is worth the price.
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I didn’t pick that up from the question, Ted, but you might well be right.
Mike[/FONT]
One small thing I’ve tried in terms of looking for other people traffic is via Alexa on their site page and click on Clickstream, it will not give you all their traffic but will show a good bit of it displaying where their majority of traffic comes from