Online Marketers always try to do an online competitor analysis to get to know which websites target the same keywords as you do
To find out:
- who these competitors are;
- their page rank, …
- incoming links and value of the incoming links
- marketing techniques they use (Google Ads, linkbuilding, Press Releases, Affiliate marketing to generate traffic for them self, Social Networking, ...)
- Same site hosted in different servers, under different language related domains (.com, .de, .es, ...)
Normally, most of these info you can get with a site: operator search on Google or yahoo. Yahoo will give you a more accurate total of links into a site.
Beside, Spyfu is an online competitive intelligence application that allows you to browse competitors' PPC keywords, daily budget, bid prices, clicks/day, and other interesting PPC facts & figures. The tool is useful for researching the competition and uncovering new keywords, the tool works by scraping the search results of over half a million phrases each day and then storing them in the Googspy database. Marketers use the tool by entering the domain name of a competitor and viewing a list of the search terms that they rank well for. The tool also displays the top 25 competitors for the company that you search on. Entering a search term will bring up a list of companies that are purchasing Adwords, along with the text of their ads.
Finally, here is a link that should answer some questions: http://www.toprankblog.com/2007/06/winner-best-keyword-research-tool/