The Petronas Towers in Kuala Lumpur (Malaysia).
According to the CTBUH's official definition and ranking, they were the tallest buildings in the world from 1998 to 2004 until surpassed by Taipei 101, but they remain the tallest twin buildings in the world.
They were designed by Argentine architect César Pelli.
For more information about the Petronas Twin Towers, read en.wikipedia.org/wiki/Petronas_Towers.