Web directories like the Open Directory Project DMOZ provide a searchable source for websites organized by categories and sub-categories. Maintained by humans (at least the reputable ones) who act as editors and make sure the submission is accurate and worthy of listing. It's a massive undertaking to maintain a directory and why some require a fee for being reviewed. The premise being that you pay a fee and it does not guarantee your site's inclusion. When considering using a web directory or blog directory to publicize your site look it over and see if the categories are related to your industry.