I remember a few of them. I'm not sure that they are still do-follow because I checked them last in september 2008. You can google and find more. But these are very good ones and they are quite popular. http://www.diigo.com/ http://www.bibsonomy.org/ http://www.spurl.net/ http://www.furl.net/ http://www.clipclip.org/ http://www.mister-wong.com/ http://slashdot.org/
Here we go, just Googled these. PR 8 http://www.Blinklist.com PR 7 http://www.Mister-Wong.com PR 6 http://www.Backflip.com http://www.BibSonomy.org http://www.Diigo.com http://www.Spurl.net http://www.Furl.net http://www.Feedmarker.com PR 5 http://www.Connectedy.com http://www.myVmarks.com http://www.HealthRanker.com http://www.Jumptags.com http://www.BuddyMarks.com http://www.linkaGoGo.com http://www.Spotback.com http://www.IndianPad.com PR 4 http://www.A1-Webmarks.com http://www.Dizzed.com http://www.BookmarkTracker.com http://www.OYAX.com http://www.MyLinkVault.com PR 3 http://www.MyPIP.com http://www.SyncOne.net http://www.Yattle.com PR 2 http://www.Tedigo.net PR 1 http://www.buzztagz.com http://www.Chipmark.com
To be honest I tried many experiments with the do follow social bookmarking with all of the websites above and they had little to no seo value. I still submit to mister wong just because it is on my bookmarking list but it is not used specifically for SEO.