30 St Mary Axe
Formerly the Swiss Re building, but more commonly called the Gherkin.
This photo depicts the only curved glass in the entire building- the top dome.
Since the building isn't normally open to the public, I arranged a tour for a friend who studies architecture, and ended up learning a lot about the building that I view out my office window on a daily basis. Did you know that it uses 50% of the energy of a standard, similar-sized building? Among other things, certain windows automatically open a few degrees to facilitate the chimney effect within the building.
We lucked out with a sunny and fairly clear day- the views out to the east were fantastic :o)