Where can you get the first world of Warcraft Exspantion set. The one before the Burning crusade

The World of Warcraft expansions are as follows:

1st expansion - Burning Crusade
2nd expansion - Wrath of the Lich King
3rd expansion - Cataclysm

Those are all the expansions that World of Warcraft has. The only thing that came before Burning Crusade is the original basic game.