Alexa.com is a company owned by Amazon.com that offers remarkable data about your website and your competitors. To see the top performing keyword terms for a website go to Alexa.com/siteinfo and plug in the URL of the website you're researching. Towards the bottom of the page Alexa lists the keywords most commonly used to find the website. On the left side of the page Alexa also shows the sites which refer the most traffic to that website.
Alexa has free and paid versions. I have not dedicated funds yet to use the paid version, so I can't speak to how much better it is. I can say that the free version is super-cool.
For Heaven's sake, make sure that your giving them what they want, or change your site if what they want is not what you offer. Here's a great example of when a website is NOT giving people what they want: http://www.chathamsheriff.org/
I did research today for The ELLA Foundation, a client who helps people affected by violence, including people who are in jail. The ELLA Foundation is based in Savannah, GA, and we wanted to know how the Chatham County jail website might be addressing issues of violence and those affected by it. So, I started looking at the Chatham County Sheriff's Office website and researched it further on Alexa.com. Alexa shows that the most common searches that land on http://www.chathamsheriff.org/ are as follows (source: http://www.alexa.com/siteinfo/chathamsheriff.org):
The % numbers are the percentage of search traffic that came from that term. Pretty easy to conclude from these numbers that people who get to this site are interested in information about the jail, who's in it, and how to get money to them (viz jailatm).
Now check out the website home page to see how the organization doesn't know what people want from their website (or does not care):
This may look small on your monitor or website, but notice that the top half of the site is spent recruiting new officers. The very bottom of the page has the links to the information that is the most searched for term on the website.
Also notice, that 39% of search traffic comes from the term "chatham county jail" and the words "chatham county jail" does not appear anywhere on the page. In fact, to find information about the jail from the top navigation menu, you will need to click on "corrections".
Google search is sensitive to how people use terms interchangeably. This is referred to as "semantic search", when a word or phrase can bring up the intended result even though the search terms were completely different from the terms on the page. In this case, the web page refers to "corrections" and the "Chatham County Sheriff" and Google correctly understands this to be the website of the "Chatham County Jail".