Most (if not all) of these places allow you to create a “profile” that people will see. Inside that profile, you can (carefully) direct your traffic to either you main sites or directly to your products Paid Social Network Site
I would suggest that you interact with the networks and gently push your traffic to your main sites products.
Otherwise, you will get a reputation as a spammer and your profile deleted. So, be careful!!
Social Networking Sites
http://360.yahoo.com
http://spaces.live.com
http://www.MySpace.com
http://www.orkut.com
http://www.facebook.com
http://www.hi5.com
http://www.friendster.com
http://www.fotolog.com
http://www.livejournal.com
http://www.bebo.com
http://www.xanga.com
http://www.multiply.com
http://www.linkedin.com
http://www.piczo.com
http://www.last.fm
http://www.stumbleupon.com
http://www.broadcaster.com
http://www.gaiaonline.com
http://www.mybloglog.com
http://my.opera.com/community/
http://www.buzznet.com
http://www.imvu.com
http://www.twitter.com
http://www.slashdot.org
http://www.wayn.com
http://www.classmates.com
http://www.meetup.com
http://www.vox.com
http://www.blackplanet.com
http://www.faceparty.com
http://www.yelp.com
http://www.ning.com
http://www.secondlife.com
http://www.myyearbook.com
http://www.hubpages.com
http://www.43things.com
http://www.mog.com
http://www.reunion.com
http://www.xuqa.com
http://www.ecademy.com
http://uk.tribe.net
http://www.tribe.net
http://www.greatestjournal.com
http://www.nexopia.com
http://www.care2.com
http://www.mobango.com
http://www.couchsurfing.com
http://www.fanpop.com
http://www.gazzag.com
http://www.ryze.com
http://www.unyk.com
http://www.migente.com
http://www.downelink.com
http://www.bluedot.us
http://www.directmatches.com
http://www.zaadz.com
http://www.librarything.com
http://start.aimpages.com
http://www.dogster.com
http://www.tagworld.com
http://www.eons.com
http://www.travbuddy.com
http://www.student.com
http://www.profileheaven.com
http://www.passado.com
http://www.ruckus.com
http://www.graduates.com
http://www.meetin.org
http://www.blurty.com
http://www.takingitglobal.org
http://www.consumating.com
http://www.wallop.com
http://www.trade-pals.com
http://www.deadjournal.com
http://www.musicforte.com
http://www.mugshot.org
http://www.dodgeball.com
http://www.mygamma.com
http://www.decayenne.com
http://www.dandelife.com
http://www.tripconnect.com
http://www.bizfriendz.com
http://www.itsjustcoffee.com
http://www.mynetspot.org
http://www.babbello.com
http://www.sitespaces.net
http://www.mylocalspot.com
http://www.intellectconnect.com
http://www.udugu.com
http://www.daylo.com
http://www.refer-online.com
http://www.flingr.com
http://www.lunarstorm.co.uk
http://www.yapperz.com
http://www.listography.com
http://www.linknrank.com
http://www.communityx.net
http://www.refernet.net
http://www.vshake.com
http://www.akintu.com
http://www.100millionspiders.com
http://www.canyouconnect.com
http://www.christianspace360.com
http://www.uuswap.com
http://www.mixednutz.net
