Top 15 bookmarking sites 2013.

www.slashdot.org
www.reddit.com
www.raaas.com
www.squidoo.com
www.stumbleupon.com
www.delicious.com
www.digg.com
www.technorati.com
www.folkd.com
www.diigo.com
www.metafilter.com
www.newsvine.com
www.blinklist.com
www.bibsonomy.org
www.hotklix.com

Hope this list will help you in doing seo. best of luck.