The Burj Dubai by SOM hasn´t been finished yet, but it´s currently the world´s tallest structure. Meanwhile, the Shanghai World Financial Centre by KPF has been opened a few weeks ago, which is (as for now) the tallest building in the world when it comes to roof height with 492m (1,614.2ft). The Taipei 101 in Taiwan is 509.2m (1,670.60ft) if you count the antenna, but its roof is only at 449.2 m (1,473.75 ft).
The building took almost 11 years to be completed, delayed by the Asian Financial Crisis of 97-98 and change on design, but it was finally opened to public on August 30, 2008. You can see an interesting tour of the building on the video posted above.
The observatory on the 100th floor is amazing, with a transparent floor.
Also, I found an interesting documentary by National Geographic on the construction of the World Financial Center, posted it below. Enjoy!