As mentioned in rand al'thor's answer, [Chakoteya][1] is very useful, but if you're interested in the original scripts (with scene directions and such) rather than transcripts, you can find all the scripts for the movies, TNG and DS9 (but few or none for other Trek series) at [st-minutiea.com][2].

Incidentally, if you don't already know, Google does allow for restricted searches of all the websites whose URL starts a certain way. For example, if I want to search all the Chakoteya pages for a certain word or phrase, I can [put the search terms into the Google search bar along with site:www.chakoteya.net](https://www.google.co.uk/search?&q="get+the+cheese+to+sickbay"+site:www.chakoteya.net).

If I’m looking for a phrase, it should be put in quotation marks in the google search, so Google doesn't just look for the individual words. And if I want to search just within a particular Trek show such as TNG or Voyager, I can use a more specific URL beginning, like site:www.chakoteya.net/NextGen or site:www.chakoteya.net/Voyager.

  [1]: http://www.chakoteya.net
  [2]: http://www.st-minutiae.com/resources/scripts/