Blizzard has announced today, the beginning of the endless World of Warcraft trial, which will let players play up to Level 20 with as many characters as they would like.
If the game interests you after playing it for a while, you can continue your game by picking up the vanilla game and the first expansion pack, for the price of $20.
The Burning Crusade expansion adds two more races and will allow you to play until you reach level 70 cap. If the game continues to interest you, you can then purchase, the final two expansion packs, Wrath of the Lich King and Cataclysm.
If you already own the vanilla game, you can download Burning Crusade for free. This seems to be another attempt by the Blizzard to attract the new players as it prepares itself for the release of yet another touted WOW Killer, Star Wars: The Old Republic.