Here is a list of more than 130 Social bookmarking sites even sorted with their PRs .. Let me know if you have tried these and if you get any other list to share. visit here http://ammuseo.wordpress.com/ Thanks
Never over do with social sites instead post to best 25 sites and get traffic. I like this list it has 25 best bm sites: http://totalaffiliates.com/25-bookmarking-sites-to-get-traffic.html