Special purpose search engines, for:

• thematic domains, like:

  • scuba diving

  • ... hotel reservations, flights, shopping ...

  • science

• geographic domains (regions, countries ...):

  http://home.inter.net/takakuwa/search/search.html       lists 3,105 search engines

• special services:

  • meta searcher (MetaCrawler, MetaGer ...), InfoVis/Clusterer (Kartoo)

  • open source projects: DMOZ, Wikipedia, Nutch