Student blogs with 'total' teacher control is always the bugabo. We want students to create, and post, but teachers want control. What this means, is that now you must review each students' posts and returned comments before they become public. This can become a HUGE chore. Another consideration is whether to make student blogs public or just within a community. I say make the world their audience; deal with any inappropriate posts as real-life learning experiences. It's what they will experience outside of school (and probably already have) for sure.
In short, it depends on what you're looking for. Here are some I've used or explored:
Google Apps EDU - while this is not set up to provide for teacher moderation, I'm hoping to try this out this year as we'll have student accounts set up so students can make posts to others blogs and their username will be recorded.
Weebly - sign up for educator account and you can create classes with students. Students can create pages and blogs. Easy to use. I have not used with a class, but know of several teachers who do and love it.
Blogmeister - can be set up to have complete control over student posts and comments. A bit cumbersome to use. Have to sign up for school, then create teachers and students. Does allow for moving students from teacher to teacher as years progress without loosing students' posts. And automatically puts all student accounts on teacher page. I've used this one with 1st grade teachers.
I looked at this one early on, but never used with students. It had some challenges, but I don't recall what they were, and chances are they have remedied them by now. Worth checking out.
A very powerful blog site. You see it used by lots of folks. To get the good stuff, though, you've got to pay. But well worth it if you've got it. They provide tons of support.
This is yet another option. I have a couple teachers here using to provide discussion forums. It does allow moderation, but students must create their own accounts (though this might change if it becomes available within Apps EDU).
For some additional blogging resources, of which there are many, I maintain a page on my site that I continue to add new resources to when I discover them. There are many great educators with tons of great ideas for different age groups and styles of setting up, getting student/community/etc. involved in blogging.
Blogging is a great way for students to realize an authentic, potentially global, audience for their writing.