Top social bookmarking sites such as reddit, delicious, stumbleupon, and others are the main ones you should be focusing your efforts on when managing a social bookmarking submission campaign. The thing about social bookmarking that makes it so difficult is not only updating your sites list, but the submission process itself. It can be time consuming, which is why we go with Bookmarking Beast http://www.bookmarkingbeast.com . They submit to all the top notch social bookmarking websites, but they also submit to hundreds and thousands of other websites to get you some great backlink diversity and more eyeballs on your website.