The most popular search engines are Google, Teoma, Alta Vista and MSN. You mustn’t forget that companies that create search engine technology like Inktomi and Alltheweb, also provide results for some of the major search engines. Inktomi, for example, powers Hotbot. Another thing to remember is that most search engines provide primary and secondary search results to other search engines. One of the better search engines, and relatively new, is Teoma.
There has been a lot of consolidation over recent years and this has seen the disappearance of many search engines. The simple fact is that you have to target the major ones to get listed. If you’d like an overview of how the search engines work, take a look at Bruce Clay’s Search Engine Relationship Chart