A sub-domain for each user blog
Maybe a combination of blog module and Subdomain module:


  Automatically creates subdomains and places content on them. There are
  4 modes:
  
  User: e.g. "Mary" and content at http://mary.example.com
  
  Taxonomy: e.g. "Seattle" and content at http://seattle.example.com
  
  Organic Group: e.g. "MyGroup" and content at
  http://mygroup.example.com
  
  Content type subdomains: e.g. "News" content at
  http://news.example.com