Google, Bing and Yahoo
The "Big Three" of search engines in Europe and the USA are normally recognised as being Google, MSN, and Yahoo. Each of them has an American-based original page using a .com address and further sites specific to other countries - for instance Google.co.uk is the address for the British version of Google, MSN.fr is the site for the French version of MSN, while de.yahoo.com is the German version of Yahoo. Normally in the UK if you try to access the .com versions you are automatically redirected to the UK versions. Although it might be expected that the "world" results in the UK versions would be the same as the .com results, this is not usually the case.
Google is currently the largest and most popular of the big three and the one that most businesses try hardest to get highly ranked in. Because of this it is also the target of most of the attempts at spamming, and in attempting to rectify this it sometimes makes radical algorithm changes that can on occasions punish the innocent as well as the guilty. Its ranking system is the most complicated of all the engines and its "unique" feature has long been the major influence of links on its results. While the PageRank system seems to have been downgraded in importance over the last year or so, linking is still a fundamental part of the ranking system. Sponsored results are provided by its own Adwords system.
Yahoo are a major online presence through their Yahoo mail system and YahooGroups community system. Their commercial success allowed them to take over a number of important search engines including FAST, Inktomi, and AltaVista and to integrate them into its own system.
Bing currently holds third spot in the hierarchy. Run by Microsoft it has had many names and rebrands and was probably best known as MSN. For a long time it used results taken from the Inktomi engine, but when that was taken over by Yahoo it stepped up its efforts to bring its own search system on-line. Having begun to mature in its results, in Autumn 2006 it switched over once again to the Windows Live system being developed for inclusion in Windows Vista. Most recently it was completely overhauled and rebranded as Bing with various improvements in the layout and feature and apparently another major algorithm change. As yet the results seem to be inconsistent, a subject I blogged about in Sept 2009 - How mature is Bing.
In addition to these there are a good many smaller search engines, although many of the best known ones are actually now either owned by Yahoo or get their results from Google, so they no longer have a significant separate importance in terms of results. However some of the latter set are important companies which may change their allegiances in the future.
Some search engines are international while others are devoted to individual countries. A selection of these are mentioned under International Search.
Ask (previously known as Ask Jeeves)
Ask used to be something of an oddity in the search world due to its attempt to use natural language searches rather than keyword searches. Its results were often radically different from other engines. It has its own index and includes results from the Teoma search engine, both of which use a different ranking system to any of the other major engines.
In the last year or so Ask has gone much more mainstream and has been attempting to muscle in on Google's market. Although it now has an excellent interface - handling "universal search" rather better than Google - and is favoured by many industry commentators, it has failed to get much above 1% of the US search market share. This is rather a pity as its results sets are often excellent and a genuine competitor to Google is badly needed. Ask also seem to take personal privacy issues rather more seriously than some others.
Alta Vista
Alta Vista is perhaps one of the best known names as it was one of the first to make a major impact on the general user. Originally deployed as a demonstration of the power of the Digital Equipment Corporation servers on which it was based it became very popular until it started to show more and more adverts in a way which many found made it difficult to use. There were also issues of poor search results at times - I can recall a period when the first few hundred results on any search were filled with multiple references to Amazon database pages. At the time it was losing users Google was just coming to prominence and with such a clean interface and lack of adverts it soon overtook Alta Vista and the latter never regained the lost ground. It is now owned by Yahoo and the results are entirely taken from the parent company. There is however a suspicion that it only uses a part of the Yahoo index so results may not be identical to the Yahoo site.
AlltheWeb
AlltheWeb was a fairly major player until it was taken over by Yahoo and somewhat sidelined. It's results were originally based on the FAST index but it now also draws its results from Yahoo. It does have a rather different interface from Yahoo and it is one I often turn to when I can't find what I want on Google.
AOL
AOL, by virtue of its size as a company and the number of its customers for its ISP services has always had a fairly important impact on the search world, but more for the choices it makes about who to use for its main results feeds. Like a number of ISPs who offered users its own search system it used bought-in results from one of the major search engines and gave these results its own slant. For some time now it has used Google data and there has recently been an agreement between the two companies which will see further cooperation.
Netscape
Netscape were at one time a major opponent of Microsoft in the "browser wars" and a major ISP, and thus their choice of search results provider was an important factor in deciding who was top dog. They were absorbed into the AOL organisation a few years ago.
Hotbot
Hotbot were another important engine at one time using Inktomi results, but they are now part of the Terra Lycos group and offer a choice of using either Ask Jeeves or Google results
Lycos
Lycos' main site uses a lot of paid results at the top of it's listings but uses Ask results for its main organic results.
Abacho
Abacho are a pan-european company and may be worth paying attention to if you are targeting European countries.