Google is the big one, but don't forget that you can also search Images, Video, Maps, News, and more. You can also use some specialized keywords to get specific information, such as adding the word 'define' before a word to get definitions from web dictionaries, convert measurements from one unit to another, or get movie times locally. There are also symbols: use ~ (called a tilde) to have Google search synonyms (money=currency) AND highlight the searched terms in bold, or "" to search that exact term or phrase (no variations).
Bing is the successor to Microsoft's Live Search.
Yahoo! is a popular search, and also has searches for Local Information (businesses, etc.), Images, Video, News, and more, including one of the original question sites, Yahoo! Answers.