As you likely know, the official launch date is 9/25/2012.
An Enhanced Version is available for $60, but doesn’t offer much (in my view.) ibtimes says there’s an $80 version as well, with DVD, sound track, art, and more stuff. Sounds a little more interesting to me.
You should be able to buy it all over the place, including the Bliz store and Amazon. Some sellers might have incentives.