Actually the tallest building in the world is in Taipei, Taiwan.
"...the Council on Tall Buildings and Urban Habitat defined four categories in which the "world's tallest building" can be measured:
1. Height to the structural or architectural top (including spires and pinnacles, but not antennas, masts or flagpoles)
2. Height to the highest occupied floor
3. Height to the top of the roof
4. Height to the top of antenna
On April 20, 2004, the Taipei 101 in Taipei, Taiwan was completed. Its completion gave it the record for the first three categories.
Today, Taipei 101 leads in the first category with 509 m (1,671 ft); in the second category with an occupied floor at 439 m (1,441 ft); and in the third category with 449 m (1,474 ft)."
Apparently, the CN tower is the tallest free standing structure, but it doesn't count as a building because it doesn't have floors throughout.
But I still laughed
http://en.wikipedia.org/wiki/World's_tallest_structures