Well ive always being saying that Google is a webmasters best friend, heres more proof. Google has provided a number of tools for SEO and helping webmasters to provide better content by understanding how and what has more demand in the web world. Below are a list of tools that would help you do the same.
Google Webmaster Tools: Google Webmaster Tools is a no-charge web service by Google for webmasters. It allows webmasters to check indexing status and optimize visibility of their websites.
Google Analytics: Google Analytics (GA) is a free service offered by Google that generates detailed statistics about the visitors to a website. Its main highlight is that the product is aimed at marketers as opposed to webmasters and technologists from which the industry of web analytics originally grew.
Google Website Optimizer: You can try different versions of your site that will be randomly displayed to visitors, allowing to obtain sufficient data for us to make decisions about design changes.
Google Zeitgeist: A Trends showing tool which shows what is Hot and what is Not on a year basis.
Google Trends: Allows you know how much or little that is sought a sentence or word in Google, allowing to compare curves between them. There are only the most popular.
Google Insights for Search: Allows you wanted to see what is a phrase or word, regardless of popularity.
Google Traffic Estimator: Made for Adwords, allows us to draw conclusions about the views that a particular word generates.
Google Keyword Tool: Also made for Adwords, we can help you choose the best words in our texts to attract more visitors.
Google Search Tool Based Keyword: Another option that allows us to find keywords on specific websites.
Google Ad Planner: For statistical profile of visitors to any website.
Let me know your views and if you have more.