1) For current players that haven't bought Cataclysm:http://us.blizzard.com/en-us/news/
"If you or a friend are currently playing Wrath of the Lich King and haven't yet experienced the content Cataclysm has to offer, you can sign up now to play a 10-day free trial version of this latest expansion for World of Warcraft.
"During your free trial, you'll undertake epic new quests, explore the reshaped and newly discovered lands of Azeroth, and see the world from a whole new perspective as one of the shape-changing worgen or crafty goblins.
"To participate, you'll need full versions of World of Warcraft and the first two expansions, The Burning Crusade and Wrath of the Lich King. Note that a character of at least level 78 is required to explore the new, high-level zones. More information on the 10-day free trial is available in our FAQ
. We look forward to seeing you in the new Azeroth!"
2) If you haven't ever played the game, bug a friend that has the current release. There are two free trial coupons in the box.