Building links by posting on blogs

I sell SBI site builders and want to post on dot follow blogs for link popularity,, traffic and compatibility.
How do I find them. I would prefer a free method and one that dose not involve downloading something that opens in winzip unless it is easy to set up and instal

 

You can use commenthunt to search for dofollow blogs: http://www.commenthunt.com/

 

The comment hunt site looks like a great idea but if you buy comments who post them and how does it work.