Ok, so here is the process i used to get a "Free BC CD-Key"
1.) Go to Walmart/CompUSA (or anyother place you can buy WoW CD-Keys and Gamecards)
2.) Buy the BC Key or Gamecard (doesn't matter which one really since they both are 29.99)
3.) Walk out of the store and go into your car, or walk around if your near a mall or something.
4.) Open the box carefully, being sure not to destroy the seals on the outside.
5.) Take a pic, or write down the CD-Key(or gamecard)
6.) Go back to the store around an hour or two later, and call up a friend before you walk in.
7.) Goto the return area and while on the phone with your friend talk to the return person and tell them you bought the game by mistake and you meant to buy the Gamecard. (or vise versa)
8.) Go and pick up the Gamecard/CD-Key
9.) Walk out and go home. Or goto another Walmart if you want to do this again.
Using this you will be able to get a CD-Key and a Gamecard for the price of one. Its not really free, but its like a buy one get one free.
If this is a repost sorry