Hi,
It can be helpful, but the best results definitely come from blogs that are pickier about what comments & links they publish. If the SEs realize that each post ends up with 100+ out bound links, you're probably not going to gain a lot of credibility from posting there.
visit this blog you can find the list of dofollow blog
http://webmaster-ravinder.blogspot.com/2010/12/free-auto-approve-do-follow-blog-list.html
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