Social bookmarking websites rarely do "do-follow" - it's too tempting for spammers and they would be passing a lot of juice to external pages...
Check this great list of free sites which can give you authoritative links from credible sites. http://www.cucumbernebula.com/blog/a-list-of-link-building-lists/
I have Some High PR do-follow Social bookmarking Sites Here is Do-Follow List http://solidealfr.com/ pr4 http://stictactest.com/ pr4 http://legal-mentoring.com/ pr4 http://mak-torun.com/ pr4 http://boxwoodproducts.com/ pr4 http://scienceskillsmatch.com/ pr4 http://hang-bag.info/ pr3 http://webdet.info/ pr3 http://drjwg-mn.info/ pr3 http://terredenergies.info/ pr3 http://poirrier.info/ pr3 http://onwardstudio.info/ pr3 http://traversoandpartners.info/ Pr3 http://columbialabels.info/ pr3 http://leilasadeghi.info pr3 http://autoanttila.info/ pr3 http://www.1000question.com/ PR4 http://www.tattoo-ego.com/ PR4 http://ctctrade.com/ PR4 http://powerofinfographics.com/ PR4 http://ebi-hotel.com/ PR4 http://nextgenstreetlight.com/ PR4 http://offpistjon.com/ PR4 http://nurseconnectsoftware.com/ PR4 http://didcodyscore.com/ PR4 http://collegeadmissionnews.com/ PR4
reddit.com stumbleupon.com slashdot.org tumblr.com delicious.com diigo.com designfloat.com squidoo.com wikia.com mostrawildt.com url.org stumpedia.com dropjack.com tagza.com grjm.net izeby.com jeqq.com http://www.bibsonomy.org chictini.com nkjunak.com portugal-linha.net linkarena.com fashionablylatent.com bukmark.net book-marky.de quickieclick.com video-bookmark.com indofeed.com panamatop.com heritageweb.net govmp.net bookmarkworld.org annuaires-du-gratuit.com webmaster911.com kojaxx.com way2bookmarks.com bookmarkindonesia.com yemle.com wordsjournal.com viewcool.info usedmotorcyclesfordiscount.com acymca.net gratis-community.at This are the list of social bookmarking sites
If I were you, I wouldn't use ALL of them... Use the top 5-10 according to PR, do NOT use do-follow only... This will look UNNATURAL according to Google and it would have max benefit. 5-5 would be excellent (dofollow vs nofollow!). These TOP 10 for example will help you get ranking, while others would help you only get a FEW more visitors, but won't help you in the long run... BTW, most of them are already spammed to death with so many sites...
You must check sites before bookmarking your links that either these websites are getting traffic or ever they hit by panda-penguin updates.
My suggestion? Pick out just a few and use them. I was hit pretty hard in Penguin 2.0, so I removed a couple of thousand links from the many social bookmarking sites I was using. I suspect that Google did not see that many social bookmarking links as a positive.