Social bookmarking is an online service that allows online users to share their content with backlinks to their website. There are lot of bookmarking sites from long time. Like- Digg, Delicious are very old site for bookmarking.
Productdiary.com is a place of free SEO services where you could submit your website links for quality backlinks. It is the best directory submission service, add links, add a website, blog pages link submission, article submit.