There are hundereds social networks but submission in all of them doesn't really work. Newsvine for example ban everyone who submit their own links or submit links which they don't like. I-am-bored network allow submissions but links appear after admin approval only... Here list of social sites where submission is free, automatic, and it is hard to be banned (unless you submit really bad stuff).
http://www.plime.com/
http://reddit.com/
http://digg.com/ - of course!
http://www.simpy.com/
http://ma.gnolia.com/
http://9rules.com/
http://www.spicypage.com/ - you have to submit your site first and after share links.
http://www.indianpad.com/
http://www.mixx.com/
http://www.stirrdup.com/
http://www.linkinn.com/ - somethimes they remove if they don't like.
http://www.earthfrisk.com/
http://www.sk-rt.com/
http://www.shoutwire.com/
http://del.icio.us/ - they use "nofollow" but network can provide great traffic.