Search Cloudlet is a Firefox extension from the International Software and Productivity Engineering Institute (INTSPEI) that gives users a cloud of tags to help modify and focus searches on Google and Yahoo. Once installed it will show up on top of search results and provides a simple way to tweak the original query by offering up keywords pulled from the results.
Words that appear more often in the results appear as bigger, bolder tags that you can click on to re-start the query with that word tacked on. The creators recommend dialing up the number of default search results to 100, which may make your searches slightly slower but result in a much more accurate tag cloud. This can be done from the user preferences in both Google and Yahoo.
In addition to standard Google and Yahoo searches the extension works on Google News both for keywords and locations. It also works for Google Blog search in a really neat way by adding tags for each author that you can click on to filter which posts come up.
Search Cloudlet is an experimental add-on and does not yet work on the latest beta of Firefox 3.1.