If you want your site to appear in one directory is imperative that you sign up manually, because it will not appear on the list. Usually the results of the search are listed alphabetically and by category. All directories have a very similar registration form to collect the data and how your registration is manual many confuse it with a classified ad site. Most are free but there are those that require a payment or those who demand a trade. It is important to repeat and stress that a directory is not a Search, therefore “not ready” websites and you can not get search results for keywords, as in a search, the information contained in a directory is organized by categories, subcategories and themes as I said before. I would say that within the most famous web directories are: Yahoo and DMOZ. But the list of these sites is not only very wide but very varied, I think it is better to log in to Google and put the next bit “directory listing” it will so many that you can not imagine. Good luck!!