GamED Academy: http://gamedacademy.com/
I can’t recommend this one because we haven’t tried it yet, but I’m intrigued. The idea is that the lessons are all in Minecraft. Kids watch, learn, and build as part of their learning process.
There are curricula for maths, history, science and other stuff too.
I’m not sure how this will work out, but my son has decided that actually having homework in Minecraft would kill his buzz, and he’d like to keep gaming and education separate for now.
If that ever changes, we might give this a try.