Charles Knight at Read/Write Web has an interesting post about the top 100 alternative web search engines. That's right, the top 100...there are many more that didn't make the list.
I took Mr. Knight's list plus my own list, mashed them together and categorized the search engines by major area. Entrepreneurs are trying everything they can think of to beat Google, Yahoo, and Microsoft Live. Here are some of the approaches and the companies that are trying.
User Interface (UI) enhancements attempt to improve the user experience and visual representation. Companies working in this area include; Snap, Live.com, and SearchMash. Another, Quintura, presents search results in a "visual cloud" that clusters results by meaning and intent. AskVox and Ms.Dewey use talking females to coach you through your search.
Technology advancements include; Hakia , Powerset , Lexxe, Mindset, Surfwax, Swoogle, which search based on meaning or intent. I have seen the Powerset demo, and if the model can scale to handle billions of documents on the web, Powerset has a good shot at breaking out and becoming a star.
Social/Personalized Search - Findory, Jookster , Swicki , Collarity, and Rollyo do personalized or social search that present results based on your personal preferences or circle of friends. There are also a bunch of companies doing "tag" or "voting" based search...companies like Technorati, Digg, TailRank, and others.
Meta search engines submit your query to multiple search engines and present all the results on one screen. This has got to be the most over done, and marginal category in search. Examples include; Dogpile, CrossEngine, Gnosh, GoshMe, GoYams, Grokker, Ixquick, Mamma, Mrquery, PlanetSearch, PolyMeta, Pronto, Srchr, TurboScout, Whonu, and ZapMeta.
Vertical market segment search has lots of players in each category;
Venture Capitalists, over the past 5 years, have poured billions of dollars into search engine startups hoping to hatch the next Google. There are probably more than 200 search engines today, trying all sorts of different approaches to search. Still, nothing beats the traditional big three of Google, Yahoo, and Microsoft Live.