A good place top find web 2.0 sites is on this list. They have the dofollow marked with DF. I hope it helps.
I wouldn't worry too much about the no-follow stuff. I mean, Twitter is rel="nofollow" yet if you know what you're doing on there, your links will get indexed like crazy ... primarily 'cause it's an authority site, and it's "trusted". But that was a good list, Tornado. Thanks! Jason
Please check this following link as it talks on the top do-follow social networks http://www.insertknowledge.com/2012/09/list-of-social-networking-sites-to.html
I've got a little plug for you - It's not neccessarily your typical web 2.0 social bookmark, it's more of a platform where you share content and can get revenue share as well as links - it's called triond - just google it (I don't want to post a link in case I infringe any new rules) This can earn you backlinks from high DA sites - (dofollow) give it a go! And if you 'like' me advice please let me know how it helped!
That is really good list. Actually VMOPtions have the list of all kind submission directories and bookmark websites
you should give a try with www.bloghology.org also if you have quality content you can create a Free Blog