Best social bookmarking sites (with PR of each)

Social bookmarking is really a good way to get traffic and improve your site Page Rank
the idea is simple , any one can join the site and can submit any link that is not submitted before
links to good content usually get ranked in the site and get more traffic , submitting your sit to social bookmarking sites is a way for your site promotion

List of best social bookmarking sites : PR 9 PR 9 PR 8 PR 8 PR 8 PR 8 PR 8 PR 7 PR 7 PR 7 PR 6 PR 6