WordPress.com - Not only can you install WordPress on your own sites, you can use the same software on their site and save yourself all of the technical work.

Blogger.com - A great starting site to get a taste of blogging, very easy to use.

Weebly.com - Allows you to create a site and blog, free hosting and change designs on the fly.

Blog.com - Offers free blog hosting with unlimited bandwidth for their free package, more benefits for paid members.