Seach Cloudlet is a plugin for Firefox that adds a tag cloud to Google and Yahoo! search results. While this might not sound incredibly useful, it is. Here's how it works: You enter a search term and Search Cloudlet brings up a list of related tags. Click that tag to refine your search by addind that term. For example, if you're looking for the new Battlestar Galactica webisodes, you can start by typing just one word, like "battlestar" and keep clicking links until you find what you're looking for. It's great for people who aren't always sure what keywords will be the most useful.
You can also click the Sites tab to show a list of web sites featuring content matching your query. So if you want to limit your search to, say, Wikipedia articles, just click on the Wikipedia link. The Net tab lets you limit your search by domain type, such as .com, .org. or .net. I'm not really sure how useful this feature is. And if you want the tag cloud to go away all you have to do is click the Off button.