Last year I used kidblog.org for my students blogs. They wrote about their math learning and about projects we did in math class. Occasionally they chose a topic. I am not an ELA teacher so I wanted them to use their blogs as reflective journals. Here is their work from last year http://plnaugleclasswiki.wikispaces.com/Blogs.
This year I will be doing basically the same thing. The students love blogging and I use #comments4kids on Twitter to get lots of comments. Happy blogging everyone.