Bloggers.com is a large website where bloggers can register their blog.
The helps you enhance your blog in the event you take some time to participate (that is, make sure you say something else than just, Hi! How are you? or I liked your blog!)
By participating you'll fairly quickly increase your own page rank on bloggers.com and that has a clean (rel="dofollow") link to your blog. So you'll get the benefits of the rank on bloggers.com.
Best way is to friend people and comment constructively on their own work.