The newest "world's tallest building" is under construction in Jeddah, Saudi Arabia.
The Kingdom Tower will be a full kilometer (3281 feet) in height, over 500 feet taller than the current world's tallest building.
http://en.wikipedia.org/wiki/Kingdom_Tower
BUT, here's the real irony. Guess which company is building this skyscraper...
http://en.wikipedia.org/wiki/Saudi_Binladin_Group
Here are the existing world's tallest buildings...
http://skyscraperpage.com/diagrams/?searchID=200