The entire of World of Warcraft has gone on sale, and for once, the non-ironic use of the word "epic" is entirely justified. For this week only, you can get from naught to Mists of Pandaria for $30, or €30 or £25, depending on your local currency, and this is a pretty amazing deal when you consider the regular prices. As the EU store is still only handling digital goods, those will only be available in the EU as downloads. The US, however, can pick up the boxed versions for the same price, which is pretty remarkable.
Don't forget that the Battle Chest has included Wrath of the Lich King for some time, so you're not missing out there. This is a really, really cheap way to get yourself a character leveled with Recruit-a-Friend, and indeed to pick up an Obsidian Nightwing into the mix. Or, of course, get your friends involved in the game!