The free TrackMeNot Firefox add-on takes a unique and creative approach to protecting your privacy from search engines that can create profiles of you based on terms you search for. Rather than hiding your searches from them in some way, it takes the exact opposite tack: It inundates search engines with a blizzard of background searches from you, so that no practical profile can be built because there are too many random searches. It generates those search terms from a group of RSS feeds from sites including the New York Times, CNN, and others.
It does this for the most popular search engines, including Google, Bing, AOL Search, Yahoo search, and Baidu (China's most popular search engine). If you're a Chrome user, don't despair, because the Chrome version of TrackMeNot works the same way. Every time it does a search, you see a small indication at the bottom of the Firefox screen, showing you the search term, and to which engine it's been submitted. The searches are submitted in the background, so that you can continue using your browser as you would normally, with no effect on its speed.
TrackMeNot gives you a great deal of control over how you use it, including the search engines to which you want the searches sent, the number of searches done per hour, whether queries should be shown to you or remain visible, and so on. If you'd like, you can edit the list of feeds it uses to generate the terms. Go to the Options screen, and enter RSS feeds into the appropriate box.
All in all, TrackMeNot is a great, no-pain, no-cost tool for helping ensure personal profiles about you can't be built.