I did some back links from WordPress .com, there are plenty of wordpress sites refreshed on wordpress.com everyday, There are more than 1,000 sites you can make post to make back links, some of they did not need approval, I try to submit rss to wordpress.com but can not, It seems like you have to be host by wordpress.com then your post can show on the home page. The good quality back links need you find most relative niche blog to make post. For example, I have a Chinese food recipes blog , it shows the most authentic Chinese food recipes for free, So i go to search food & cooking niche on wordpress.com, each time there are new posts, I will go to view them and try to make a post to support them, I love helping people, when you discuss with the webmaster and make nice post, they really thank you, and i can find more happy.
Is could be the same way to blogger, But so far, I only make it on wordpress, wordpress.org is another place you can leave back links, the do-follow back links, is on the support forums, ask you question, or answering the questions. After Google update 4.0, the spam way back links become non-effective, If you do need buy links, I suggest you buy the old domain relative niche and less outbound link but high PR page link. That's the best one.
Back links strategy is keep natural, make relative back links, this way could slow, but safety and stable, you did half year or years you can get benefit in your rest life.