Google Trends

Google Trends is a public web facility of Google Inc., based on Google Search, that shows how often a particular search-term is entered relative to the total search-volume across various regions of the world, and in various language.

Google Trends also allows the user to compare the volume of searches between two or more terms. An additional feature of Google Trends is in its ability to show news related to the search-term overlaid on the chart, showing how new events affect search popularity.
Originally, Google neglected updating Google Trends on a regular basis. In March 2007, internet bloggers noticed that Google had not added new data since November 2006, and Trends was updated within a week. Google did not update Trends from March until July 30, and only after it was blogged about, again.Google now claims to be "updating the information provided by Google Trends daily; Hot Trends is updated hourly."
On August 6, 2008, Google launched a free service called Insights for Search. Insights for Search is an extension of Google Trends and although the tool is meant for marketers, it can be utilized by any user. The tool allows for the tracking of various words and phrases that are typed into Google’s search-box. The tracking device provided a more-indepth analysis of results. It also has the ability to categorize and organize the data, with special attention given to the breakdown of information by geographical areas.
Google Hot Trends

Google Hot Trends is an addition to Google Trends which displays the top 20 hot, i.e., fastest rising, searches (search-terms) of the past hour in the United States. This is for searches that have recently experienced a sudden surge in popularity. For each of the search-terms, it provides a 24-hour search-volume graph as well as blog, news and web search results. Hot Trends has a history feature for those wishing to browse past hot searches. Hot Trends can be installed as an iGoogle Gadget. Hot Trends is also available as an hourly Atom web feed.