I don't normally like IGN very much, but
this was pretty informative. Note that the picture of the controller "shell" is not an official image, but it's what IGN thinks it will look like based on what they've heard. I have to say that if it's accurate, that makes a whole lot more sense than what I thought it would be (a regular controller attached to the freestyle unit by a cord). In fact, it means that now you have a traditional controller which you can also tilt and rotate for commands. Pretty neat.
IGN also says that they don't know what batteries the controller uses. I personally really hope Nintendo goes with rechargeable batteries.