Check out this review by CNet:
If you’re still going to the Google or Yahoo home page to do Web searches, you’re missing half the fun–and you’re unnecessarily exerting your fingers. Toolbar plug-ins for Microsoft Internet Explorer–and now Firefox–make it easy and fast to look up Web references without having to type in another URL.
http://www.microsoft-watch.org/cgi-bin/ranking.htm
The first number we fetch is Alexa’s traffic rank for a domain on the web. This is based on a sampling of actual traffic to that domain, and it comes from the “phone home” feature on Alexa’s toolbar…
The second number reported by this web ranking tool is a count of total external backlinks from Yahoo. An external backlink is a link to a specific page from outside of that page’s own domain. Yahoo has much better reporting for backlinks than Google…