Web 2.0 sites are a very good platform to make free blogs and build high quality backlinks for your site. Web 2.0 sites are crawled by search engine spiders very frequently and they index its new blogs also very quickly. There are a very very popular link building method that is called as link wheel which can be made effectively by web 2.0 sites. I have got a good list of web 2.0 sites where you can make your free blogs and also make link wheels. It will go according to your need.