Thanks to Aaron for building this resource about internet marketing.
Within the mindmap, he points out a resource with great information that you may have never heard about.
It's called SEO Digger. (note: SEO Digger has now moved to SEM Rush. It provides more features now as well.)
How It Works and What it Does
Type in any URL.
SEO Digger will tell you if that site is in the top 20 search results on Google or MSN and which corresponding keywords were searched for that ranking.
If you become a member, which is free to do (and worth doing), you're able to request more in-depth searches and conduct more searches per hour
This may go without saying, but this resource, combined with Compete, can tell you a lot about your competitive situation on the web.
SEO Digger can also be of value when determining how strong an established company is at internet marketing, if you're looking to launch a new venture and already know the existing competitors.