Google Insights: Google Insights takes a look at search volume and metrics over specific geographical regions all over the world, time frames, and subject categories. You can use Google Insights to research seasonal search trends, figure out who is searching for what and where, follow global search patterns, investigate competing sites/brands, and much more.
Google Trends: Google Trends gives Web searchers a quick look at the Google searches that are getting the most traffic overall(updated hourly). You can also use it to view which topics have been searched for the most (or the least) over a period of time, check if specific keywords have appeared in Google News, investigate search patterns geographically, and much more.
Google Zeitgeist: Google Zeitgeist is an annual compilation of the most popular searches worldwide in a variety of categories. This data is based on literally billions of searches globally.
Google Adwords Keyword Tool: The Google Adwords Keyword Tool gives you a list of keywords that you can filter by search volume, competition, and trends. It's a quick way to measure search statistics for specific keywords and keyword phrases.