As mentioned in my Page Strength post, SEOmoz has a Keyword Difficulty tool. The tool is used to analyze the competitive landscape of a particular search term or phrase, this tool issues a percentage score and provides a detailed analysis of the top ranking sites at Google and Yahoo.
There's a couple of manual steps involved and you have to register to use the free tool. You also need a Google API key (free) to use the tool. The tool takes a while to run so you are better off just having the results emailed to you. Other than the long wait, I like the tool and found it useful.
The Keyword Difficulty tool gives you a ranking for how competitive your keyword is, the factors involved, and the top ten results on Google and Yahoo. Then the tool gives you data on the sites that ranked in the top ten for your keyword in Google and Yahoo (ie – links to the site, Alexa ranking, mentions in Google news, pagerank, etc).
I have two suggestions for improving the tool. First, it would be nice to be able to click on a link to see where competitors are linked from. Second, it would also be useful to have your own site listed so you can compare the results of your competitors with your own site.