The eyecatching feature of the Walkie-Talkie, at 20 Fenchurch Street, is that it curves outwards towards its top, so the highest floors are larger than those lower down, giving it the appearance of a giant telephone receiver popping up through the city's buildings. Designed by Rafael Viñoly, it is due to open in April 2014, and while most of us usually have to make do with the external appearances of towers in the financial district, this time there will be a "skygarden" open to the public. The plan is that it will be free, but require advanced booking. We'll see how that goes.
There's more about the Walkie-Talkie at www.james-hobbs.blogspot.com.