Link Building in social networds

Which social networks or social bookmarks are seen by google in terms o link building?
I know the most of them use a nofollow or other system to stop SEO stuff.

Any help
thanks

 

i get most of the traffic from digg and stumble upon

 

Stumble is one which has been downplayed a lot but still DIGG is better

Let me add one named Propeller

 

Most of the familiar sites were having no follow attribute only. But still there are many sites having do follow attribute. Refer bookmarkingdir and directory roll.

 

I know about social bookmarking website which gets crawled by google and that is digg, delicious, wikio and spicypage.

 

i am also using social sites it's very helpful our website increase link and traffic.

 

The question is to find quality dofollow social bookmarking places...

 

Blog engage is a dofollow community.Submitting your posts to blog engage helps your SERP rank increase

 

you have to check them manually. most of the big ones doesnt allow any seo benefit.