See those diagonal stripes? They are support beams, and arranging them in this pattern, called diagrid, uses 20% less steel than conventional construction methods.
At left: The Hearst Tower, New York City. 2003-2006 by Lord Foster.
The lower part of the building was commissioned by William Randolph Hearst (Citizen Kane?) in 1928, and created by the architect Joseph Urban. It is now a landmark.
The addition to the building was the first skyscraper begun after the 9/11 attacks, and was completed in 2006. Its design is by Norman Foster, Pritzker Prize alum (you might know him from his Reichstag Dome, in Berlin). The Heast Tower was also New York City's first LEED Gold skyscraper.
At right: The Gherkin, or Swiss Re Tower, or 30 St Mary Axe, London. 2001-2004 by Lord Foster.
It does look like an Easter egg, doesn't it? Of its 7,429 glass panels, the only ones that are curved are at the top, where the restaurant is located. Its triangulated skin allows for column-free floor space. Its circular footprint reduces its stature at the base, slimming its profile and enhancing its appeal on a human scale (pedestrian-level). This 2003 recipient of the Stirling Prize is also one of London's greenest skyscrapers, using half the energy consumed by air-conditioned office towers.