Web Directory

  A web directory is a website where most websites present on the world wide web are classified topic-wise.For example sites like gmail,yahoomail,etc will be listed under email providers and so on.
  This can be used for research in many ways.Two ways in which I've used it are:
  1.Finding sites that feature a particular topic
  2.Find sites that are similar to a particular site.
       This can be done by searching the site name in the web directory.The search leads to the topic which features other similar sites.
   eg: go to the google directory(http://www.google.com/dirhp)
        search for google.com(http://www.google.com/search?hl=en&cat=gwd/Top&ei=wdGVS9y4Lc60rAeK3-ycDA&sa=X&oi=spell&resnum=0&ct=result&cd=1&q=google.com&spell=1)
        find the topic(http://www.google.com/Top/Computers/Internet/Searching/Search_Engines/)
  Google has a web directory(http://www.google.com/dirhp)
  And wikipedia features a list of web directories here.(http://en.wikipedia.org/wiki/List_of_web_directories)