On Facebook Blizz just posted a picture saying that Pandaria will be out on September 25 of this year. In addition, a couple hours ago the Collector’s Edition went up for pre-order (on Amazon at least), as well as the contents of the package announced.
The Collectors Edition includes:
A behind the scenes Blu-ray
The standard Soundtrack
An art book
A mouse pad
The Collector’s Edition exclusive mount and pet have yet to be confirmed, but they’re believed to be Quilen.
Right now is a great time to pre-order. I’ve waited even a couple weeks before and had to resort to Ebay-ing the Collector’s Edition at ridiculous mark-up prices near release.