following is list of web 2.0 site(update) with very high PR you can create backlink their.
I have tutorial how to do that just contact me on mail or skype and i will give you that guide it make link creation on these site very very easy

http://aleuminati.ning.com/
http://www.barcc.org/
http://www.onemillionstories.org/
http://forum.griffith.nsw.gov.au/index.php/forums/
http://www.fring.com/
http://www.spaceelephant.com/
http://www.antiproxy.com/
http://www.redbubble.com/
http://ipower.ning.com/
http://www.conceptart.org/
http://www.chineseblast.com/
http://www.tboforums.com/
http://help.irc.gr/
http://spinnerettemusic.com/community/
http://wetpixel.com/
http://wsum.org/
http://forum.boom.ge/
http://forums.edmontonoilers.com/
http://diabetestalkfest.ning.com/
http://mydeathspace.com/smf/
http://gmc.yoyogames.com/
http://community.guinnessworldrecords.com/
http://forums.devside.net/index.php
http://www.anti-malware-test.com/