Originally Posted by Site Booster

That's one of the best tools some suggest on the net. Thanks.

There's also another possibility:

1. Open a Google Account
2. Go to My Account page
3. Tick the website you're working on
4. Go to Webmaster Tools
5. You find the keywords mostly searched and those by which your site is found.

Note: This method could sometimes be very helpful specially when you want to know how people find your site and most of the times. Then, you can optimize more pages focused on those keywords.