SEO Firefox Extension

The SEO Firefox Extension is one of the most useful online marketing tools that I've run across. It's a great way to not only determine your sites' SEO strength (based on age, number of inbound links, Alexa ranking, and other factors), but you can also snoop on your competitors based on the same factors!

You need to be using Firefox, and if you're aren't already, the Extension is well worth downloading the Firefox browser just to use the tool.