Here is Aaron’s overview of the SEO for Firefox plug-in tool, which can provide a lot of competitive data for web search engine marketers, social media marketers, and entrepreneurs.
SEO for Firefox Plug-in. If you don’t have Firefox, you will need to download it.
The SEO for Firefox a) Page rank, b) cache data, c) how old the URL is, d) linkage data, e) traffic data, and f) listings in major directories. It can help you know what factors the website use to rank. It can also help you find its backlinks as well.
Also, there are 4 key buttons you can look at below Google’s search box.
Something to Remember about the SEO for Firefox plug in: there are two modes: automatic and on demand mode. You will likely want to turn off Firefox for reasons of speed.
You may also want to check out these SEO Tools for Firefox suggestions by Danny Sullivan for your SEO and SEM needs.
Alexa (not recommended highly by Aaron, due to biases, but allows you to see what sites your competitors own) Aaron mentioned that Domain will also allow you to do this.
Hitwise ($10,000 or so)
Trellian ($250 fee and $99 or a whole year for $1000)
Compete has some affordable options
SEO Digger (???) not as useful anymore
Spyfu seems more useful than SEO Digger or Key Compete (it also provides paid and organic results)
Using Backlink Analizer an SEO Book.com Tool