Beta Access Bonus Code have been spotted on Amazon.com and Blizzard.com as part of the World of Warcraft: Mists of Pandaria Pre-order Bonus.
To quote the pre-order bonus description:
“Pre-order World of Warcraft: Mists of Pandaria and get Beta Access. Code will be e-mailed within 5 business days after you place your order. Offer valid when shipped and sold by Amazon.com. This offer will be extended to all existing pre-orders and expires on September 17, 2012.”