There are 2 types of social bookmarking sites depending on the link they provide.
Both types of bookmarking is helpful to increase our web traffic. however But dofollow social bookmarking sites more effective and important for search engine results because they give dofollow backlinks to your site. also read Difference between Nofollow and Dofollow
Here’s a list of social bookmarking sites. Bookmark all of your sites in social bookmarking sites to get better results.
PR 8 Social Bookmarking Sites List
PR 7 Social Bookmarking Sites List of 2014
PR 6 & PR 5 Social Bookmarking Sites List
PR 4 & PR 3 Free Social Bookmarking Sites List
May be useful 🙂