both best buy and amazon are now offering points for cataclysm orders that equate to 10$ on another purchase. i'm pretty sure you can use the points on time cards to play even.
in other news, there's a trick to download the cataclysm stuff without your serial #, so you can just enter it and play right away when blizz unlocks it...
Want to preload Cataclysm without pre-ordering? Here's how