There are dozens of search engines out there that see a lot of use – there are hundreds, depending on what you’re looking for. Some of them are actually pretty good at helping you find specific things. However, most people don’t use them, either because they don’t know about them or because they aren’t powerful enough outside the specific subjects for which they’re intended.
When it comes to looking for absolutely anything, there aren’t a lot of engines that can really compete with the “Big Three” of Yahoo!, bing, and Google. They’re easily the most powerful search engines available, which is why they’re the dominant search providers on the internet. They search pretty much everything, even entries that are specifically placed on other search systems like YouTube (which is partly a search engine for finding specific videos and categories within the clips posed to it).
The tricky part is that lots of sites include search engines as part of what they do, but can’t reach beyond their own limits. Only search engines dedicated to that purpose can, which is why they are generally the only ones people think about. However, anyone who wants to do some powerful searching needs to include the “lesser” engines of places like YouTube, Facebook, and so on.