I had been considering buying Burning Crusade from Ebay but I kept putting it off ... over and over.
Glad I did.
Now Blizzard is selling Burning Crusade for $5 and WOTLK for $10!!!!
Cheaper than used games on Ebay and you get 'em direct from Blizzard so you know they are virus free and work.
Bought Burning Crusade this afternoon and just went to Outland. Tomorrow I will buy WOTLK. Takes a couple of hours to download BC on a cable connection .. it was 12 GB.
I believe you can order on disks also.
But if you don't have these expansions you can't use Cataclysm and at these prices now is the time to get 'em.
Once Cata comes out the price may go back up.