If you are looking for good examples of pupil-created blogs then go take a look at the Blog the World Cup project.
The idea is brilliantly simple: there are 32 nations in the FIFA World Cup and there will be 32 blogs on the site, one for each competing nation. Each blog will be managed by a different class (or school) with each one allocated a country at random.
You can get a list of all the different blogs here. Take a look and see if you could do something similar with your pupils.
Kudos to John Sutton for setting up and organising the project, and well done to the classes involved for their work so far!