Some popular ones are Altavista, Google, and Excite. Metasearch engines take your search words and feed them through other search engines, then give you the results from many engines at once. What's more, if you run exactly the same search on five different search engines, you're likely to get five very different sets of results. Each search engine works differently. Depending on how you word your search, it looks for information on your search words using different methods.
Some search engines are better than others for certain types of searches.
The best thing you can do is learn how each search engines works, and decide which would be best for the type of search you are doing. If you're using a search engine and you're not having any luck finding information, try reading through these helpful guides. You can also use the following links to pages which compare different search engines and explain how they work. This page, created by a Kansas City librarian, is a brief introduction to some of the most popular search engines. It includes a nice chart comparing the features of different engines.