There are many but my suggestion is to use Google+ social networking site, It is Google's site with 9 PR with 1 Alexa Traffic Rank and give do follow back links and most important thing is it index instant.
I have already been bookmarking for a long time but We are uncertain which 1 is. I actually do possess personal favorties just like stumbleupon, folkd, and netvouz.
There are Many social bookmarking sites are Available. High pr Bookmarking sites are the Google +, Twitter, Facebook, LinkedIn, Pinterest, stumbleupon, folkd, Reddit etc.