Alexa Search (which is part of Amazon) tends to be regarded as an imperfect tool, but it's still extremely viable, useful and free (although many bloggers slag it off, I know analysts use it as another info source).
- Geographic user report — See what percentage of users for a site comes from each country.
- Traffic rank by country — This one is interesting to actually see your site's ranking in different countries.
- Reach percentage — Instead of reporting the confusing "reach per million" they were doing before, they now show what % of the total web user base a site reaches.
Alexa utilizes web usage information, which tells us what is being seen on the web. This information comes from the community of Alexa Toolbar users. (more about how they've refined this).You can use it to get some idea of where you stand compared with other sites, amongst it's other uses.
Hitwise uses a combination of anonymous web surfing data provided by ISPs in various countries and its own panel-based measurements to determine which sites are most popular on the web.
I have compared raw stats (from other sites) and found the Alexa comparison closer than the Hitwise one, although the industry tends to like Hitwise: they do publish lots, including some great analysis (see LeeAnn Prescott)
More Alexa Site Information - Alexa has built an unparalleled database of information about sites that includes statistics, related links and more. All of this information can be found on Alexa's Site Overview pages, Traffic Detail pages and Related Links pages. To access thes pages, simply type the URL of any site into the Alexa Search box.
In addition to the features mentioned above, Alexa also has Movers & Shakers (sites jumping in traffic) Hot Searches (what people search for) and lists of Top Sites in available by language or categories.