|Alexa provides a free toolbar from which users can glean info about the websites they visit, block annoying popup ads, find related websites, and directly contribute to the rankings themselves. The toolbar provides statistics back to Alexa which they then use to rank the websites on both 'reach' and 'page views'. The geometric mean of those two rankings comprise a website's overall ranking. The toolbar currently supports only Microsoft Internet Explorer.|
Sitereview.org is rated #186,597 as of today but, unfortunately, is on a downward slide.
(*)some would say the title should be 'ranking the biggest' of 40,000,000 sites, but each pageview by an Alexa toolbar user counts as a vote so 'biggest', as used here, is sort of a democratically-determined quality ranking.