I recently stumbled across an interesting research tool called; G-Metrics .
This is a web based system that allows you to track changes in the number of search results returned by Google for a specified query. The service is powered by the Google API, which G-Metrics uses to poll Google daily for the number of results returned for each search term in its database. The service creates time-line based progression charts detailing these fluctuations. Another nice feature of this tool is that it is subscription based; all you do is sign up for a free account and you can store and track multiple search terms, which are updated daily with new information. G-Metrics presents an original and unique service to the world of search engine marketing. Definitely worth taking a look at.