Unified Search is a Firefox add-on that allows you to view various search engine alternatives in the right-hand side of your usual results. The alternative engines are configurable in the options area of the Tools > Add-ons menu at the top of your browser. Unified Search currently offers five additional search providers - Bing, Wikipedia, Stumbleupon, Wolfram Alpha and Delicious. You can enable or disable any of them, either from the configuration window or by closing them on the webpage.
Obviously, some search terms are better processed by certain search providers, so the quality of your searches will depend on what you search for and the provider you use. Unfortunately, Unified Search only offers 5 extra search engines at the moment, which is a bit limiting.
That said, Unified Search is a handy tool, and definitely enhances searches. If a search turns up particularly good results in one of the additional engines, you can pop it out and view in a new tab. Hopefully future versions of Unified Search will have more search options and enhanced configuration options. Even so, the current version is very usable and a good addition to any user's browser.
Unified Search is a great way to maximize your searches.